Wednesday, December 30, 2020


Often, when you discover a vintage Honda 250 or 305cc twin available for sale, it is lacking the title or other necessary documentation. Depending upon the state or country's requirements, you will find it necessary to "create" some paperwork for registration purposes. The first step in this process is to determine the correct year of production.

On early-'60s (1960-64) Honda 250-305cc twins, this can be pinpointed accurately, using the frame/engine serial numbers, found at various locations on the bike. You will notice that Honda's serial numbers carry a letter (or two), followed by a number (i.e. C or CA77, CB72, CL77, etc.). The "72" designation (as in CB72) denotes 250cc models, while the "77" designation signifies 305cc models (for instance, CL77). All pre-1961 (C70-71 & C75-76) engines were "dry-sump" design (separate oil tank). After 1960, the C/CB/CL 72/77-series engines were all of conventional "wet-sump" design (all oil carried within the engine).

Honda's frames were classified as either: C "Dream" (touring-style); CA or CE (US-only versions of "Dream" touring models); CB, "Super Sport" road models; CL "Scrambler" (dual-purpose); CR (production roadracing models); and CS, the "Dream Sport" (usually featuring high-mounted side pipes). The C (or CA, CE or CS)-series "Dream" models have stamped, sheet-metal frames, forks and swing arms, riding on 16" wheels (except CE71s) and equipped with "leading-link" front suspensions. All other models (CB and CL) will have tubular-type frames and swing arms, fitted with 18" (CB) or 19" (CL) wheels and conventional, "telescopic" front forks.

For 250-305cc street bikes, built before 1965, the identifying process is relatively easy. In the late '50s and early '60s, the year was often coded within the serial number (i.e. C71 59 12345); the center numbers denoting the year ( in this case 1959). Later, the first digit of the 5-digit frame (and 6-digit engine) number was used as the year code (i.e. CB72-11123, a 1961 250cc Sports model). Here's an overview of the three most popular models:

CB models: The CB72/77-series (known as 250 Hawks or 305 Super Hawks) were numbered as follows: '61-63, first digit in frame (five digits in '61-62; and six digits in '63) and engine serial number (all six digits) was year of manufacture (i.e. CB72-1XXXX; CB72-2XXXX or CB77-31XXXX frames and CB72E-11XXX; CB72E-21XXX or CB77E-31XXXX engines).

In '64, frames and engines both started with 100001 (both six digits) OR 4XXXXX numbers. The 1965 models started with 1000001 (seven-digit frame and engine numbers) and continued in that fashion. Generally, the frame and engine numbers are within 150 numbers of each other or less (often within 15 numbers), if they are the original factory pairing. One possible reason for the mismatch is that Honda would pull engines from the assembly line and dyno-test them for durability, performance, and any design/manufacturing flaws. Interestingly enough, I once owned a '64 CA77 which did carry matching 108106 frame and engine numbers; a very rare occurrence in my experience! I have noticed that, in general, the '64 engines and frames are more closely matched than for other years.

Getting back to the CB's, there are several variations, other than the "regular" Hawk/Super Hawk versions, but they were never sold in the US. The vast majority of CB-series bikes all seem to be normal Type 1 (180 degree crank) engine versions. Then, you may also find the odd CP77 frame, which may or may not be a "Police version," (which is usually called a CYP), as well as a CBM72, which has high bars, turn signals and a Type 2 (360 degree) crankshaft. The actual CP77 Police models had a different second digit in the serial number to separate them from the non-Police CP77s.

There are also "domestic" versions of CB77s with Type 2 engines. (I owned an original '62 model carrying CB77E-260474 and CB77-62-60453). Deviations from the "normal" numbering sequence usually denote models for specific countries or special applications. Genuine CYP77 Police bikes are all white and have a single, round speedometer, rather than the oval, dual speedo-tach gauges of the other models. Some Police models had 17" wheels, front and rear. Police versions have crash-bars, turn signals, solo seats, a rear rack, special lever brackets for the siren controls, patrol lights, and that great big, screaming, cable-driven (off the rear wheel) siren.

From 1965-on, there is no definitive break between the years 1965, 1966 and 1967, that I have been able to discover. Although the chrome-fendered CB models, with the "oval" tail light, were introduced from frame number 1056084 and onwards, which was at the end of the production run in 1967. The TYPE 2 aluminum fork, which appeared at CB72-1005228 & CB77-1030130, seems to be found on all '66 and later model year US bikes, according to their wiring harness tags. However, the "domestic" CP77 models featured this fork design in '65, a year before the US models received theirs. Total production for this period ('65-'67) was 56,432 (frames), so you can roughly divide that figure by three, yielding about 18-19,000 per year. If the type 2 fork bikes were all '66 models and later, then they made 30,130 1965 models and only another 26,000 more in 1966-67 combined. CB77-1056432 was the last CB77 made, in 1967.

Early models of the '61-series CB engines (and C/CA models) used a "rear breather" crankcase design and the first 280 bikes had a single-leading shoe front brake. There are three different crankshafts, three transmissions, two series of pistons, three series of camshafts, four different MPH speedometers (running in two different directions), early steel and late alloy fork assemblies, three different taillights, three different fork crowns, etc. etc. for the CB-series bikes. This is why you must always check your engine and frame numbers before ordering parts! At a distance, they all seem to look alike, but there are major differences between the years.

Sometimes, the original engines have been swapped with other CB or sometimes CL engines. I have even seen CA engines in some CB chassis! CL engines are not equipped with electric starters but can be retro-fitted with CB or CA starter motors and starter clutches, for CB installations. Or the CB engines can be relieved of their starter motors and then installed in a CL chassis! CHECK THOSE SERIAL NUMBERS CAREFULLY if you are ordering parts or doing a "correct" ground-up restoration!

CL-72 models: CL72's (250 Scramblers) were made from 1962-66, with CL77's being produced from 1965 through 1967. Bikes built through 1962 had 5 digit serial numbers (frame) and 6-digit engine numbers. Again, the first digit in the 5-digit series (6-digit in '63) is the year of manufacture. Thus, a CL72-21977 (example) is a 1962 model. It got confusing in '64, with an early bike series starting with CL72-1100001 thru 1109459 numbers, followed by CL72-4000001-4003437. The CL72-1000001 and-up numbers (all seven digit) were '65-66 models.

CL 72 models made after CL72-1008851 bikes had alloy Type 2 forks, big brakes and steel fenders and were made in late-1965, probably when the late-'65 (or probably '66) CL 77 models received their alloy forks and big 8" DLS brakes. CL72-4001597-4003196 and CL72-1000001-later models had rear brake cable anchored to the frame, instead of the cable receiver on the end of the swing arm bolt, which was seen on all earlier versions.

All 250 Scramblers, built through CL72-1107409, have "double-eye" shocks and a matching swing arm. Shocks with clevis ends on the bottom were used, thereafter, on the CL72's and all CL77 models. The slip-on exhaust silencer seems to have been introduced with '65 models. Later versions were welded onto the upper pipe. There are at least three sets of exhaust pipes/mufflers for the CL-series machines.

The CL77s: The 305 Scrambler models, CL77-1000001 to 1014495 were built as '65 models and were equipped with CL72-style steel forks and the same "small" 7" SLS Bikes after CL77-1014495 had 8" DLS brakes, similar to the CB77, but the front wheel is mostly derived from CB450 parts. The chrome fender bikes with the "oval" taillight started production from CL77-1043098 ('67 models). The "CB450" headlight, with bulb screw adjuster, began with CL77-1042143. From CL77-1033482, the rear shocks used an improved rear shock cover with a larger collar design. Longer exhaust heat shields were used from CL77-1046212 onwards.

The rubber-mounted seat and cushioned front footpegs were introduced from number CL77-1033482, along with an appropriate frame change to accommodate the redesigned forward seat mount. Front fenders and stays were changed, with the introduction of the Type 2 (aluminum) forks at CL77-1014496. A modified crankshaft with larger splines was begun at CL77E-1043132.

C/CA "Dreams": The C/CA-72/77's serial number pattern seems to be much the same as the CB-series. Of course, ALL C/CA engines are Type 2 (360-degree crank) engines. While "Dream" frames often seem to have no serial numbers, they are normally found in a location on the left side of the frame, behind the engine, below the swingarm pivot, and next to (sometimes under) the footpeg mounting bracket. It is an obscured area, often covered with grease and dirt. Many U.S. CA77's are stamped CA78, but the engines are all marked CA77. '61 and early-'63 models had different styling on the tank and chrome side panels, as well as a myriad of other smaller details concerning the handlebars, cables, fenders, seats, plastic side covers, etc. The CA78 models are often called “Late Dreams.” “Early Dreams” differed between the 250 and 305 models, mostly with the fuel tank designs.

All Dreams, through 1965, used a tall, thin, wide 12v battery (6v on dry-sump models), which was then superseded to the CB-type battery. The frame's battery tray, tool tray, and side cover were all modified to accommodate this design change. Seven-digit serial numbers commenced in 1965 on Dreams, too.

Almost all models, sold outside of the U.S., had turn signals (winkers) factory-installed. There are several different versions of "winkers," which correspond to the legal requirements of different countries. Sometimes, you will find 250-305 models registered as '68-69 models, but remember that they ceased production in '67, to make way for the CB/CL 250-350 models introduced in 1968!

The final way to date most complete, original bikes (that haven't had a wiring harness fire, modification, or some similar misfortune) is to check the harness between the steering head and the battery connectors (usually somewhere under the fuel tank) for a small white tag, attached to the outside of the harness wrapping. It will usually show both the part number of the harness, often including the model and THE DATE! It is the date of manufacture of the harness, but almost always corresponds to the date of the bike, too, but we have found exceptions to that rule, as well.

Well, so much for a "brief" history of dating Honda "big twin" motorcycles, produced in the early to mid-'60s. Starting with the 1970 models, U.S. regulations required manufacturers to show the month/year of manufacture of all motorcycles. This ID tag, which includes the frame serial number is usually found on the right side of the frame's steering head. Since 1981, the 17 digit VIN codes have been standard on all motorcycles. They can be decoded too, but that is another story.

Bill Silver (aka MrHonda)

Sunday, December 13, 2020

The Classic Honda used bike minefield… CB/CP77

The line from Forrest Gump that goes, “My mom always said life was like a box of chocolates. You never know what you're gonna get.” certainly applies to prospective purchases of vintage Honda motorcycles.

Unless you are buying from the original owner who has all the service records and a list of mods or damage repairs, you can never really be sure about just what you will find when you set your eyes on that rare bike that you have been lusting for during the last few years.

Case in point: I was helping a friend try to track down a black Honda CB77 Super Hawk to match is original black CB160. I had recently helped him market his CB450 Black Bomber so now he was hunting a black Super Hawk. I had sold a couple of really nice bikes in the past two years, but it seemed like very little was out for sale in the past few months. Hoping to avoid a blind purchase of some bike that was far, far away, an “opportunity” passed though my searches that appeared to be the black CB77 that my friend was seeking right here in San Diego County.

In the photos, it certainly appeared to be a “flat bar” CB77 of about 1964-65-ish vintage, but it was listed as a 1965 CP77 instead. The production CP77 (non-Police bike) models were never sold in the US, but they seemed to have been offered in Canada back then and a few of them migrated down to the US over the years. The model causes confusion as it might be considered the “street bike” version of the CP77 (actually CYP77) Police model. Again, a few Police models did go to Canada, but never to the US. The non-Police models look like standard CB77 Super Hawks, except that they have very high handlebars, turn signals, a sidestand, solid footpegs and the tail light that was only seen on the 1961 CB72-77s in the US.

Looking at the photos of this bike, it was obvious that the handlebars had been changed, the original turn signal switch was missing as were the rest of the winker parts. The side stand was not present and the tail light appeared to be the generic CB72 taillight used on 1963-66 models. So, in essence, the bike was reconfigured from the original CP77 roots to an early-style CB77 look.

Some of the current owner’s history was shared in that he had reworked the front forks due to some accident damage, had given it a good tune-up and may have replaced the tires. Unfortunately, the tire choices were 3.25x18 front and 3.50x18 rear which will ALWAYS upset the bike’s ability to stay steady on the centerstand.

I was requested to check the bike over prior to the sale transaction, which took me 50 miles from home. The bike presented itself as an unrestored model, which had a few dings and chrome pitting, but seemed overall a solid base to work from for someone who was willing to spend some time and money to get it back towards original condition again.

I started the engine, which sounded healty and firing on both sides evenly. In retrospect, I should have taken it out for a quick spin to check it for clutch slippage and/or clutch release issues.

After some wrangling, the owner and buyer made a deal and we loaded the bike into the back of my Tacoma for drop-off in Solana Beach, CA. By the time I returned home there was a message about what to do with the bike to get it serviceable and closer to stock CB77 shape. Obviously, the tires were top on the list and replacement rubber in the stock 2.75x18 and 3.00x18 sizes were ordered up.

The next question came up about how the steering lock works. At first the key was sticky and the lock wouldn’t move properly. With a few squirts of graphite lube, the steering lock was working fine, but the place where it was supposed to lock into was not present. A close-up photo revealed that the whole steering lock portion of the frame was cut/sheared off, perhaps in an accident. I can’t say that I have ever seen this happen before on a Super Hawk, as the steering stops for the stem contact the frame down behind the steering lock bridge portion. It was a mystery and a problem not easily remedied.

After a batch of parts had arrived, I arranged to swing by the owner’s home and dig into the project, starting with changing out the tires. The tires dates were back in the early 2000s and their oversizes caused extra difficulty in removing them from the rims. I started with the rear tire and once it was removed, there was a good bit of rust corrosion in the rim bead area and around the spoke holes. I knocked off the worst of it and wire-brushed the loose bits. I wrestled the new tire back on and prepared to install the wheel again, but saw signs that the ends of the cotter pins on the rear sprocket castle nuts were hitting something. There were signs that the cotter pin ends had been hitting the inside of the chain guard bracket, which also showed signs of being rewelded previously.

An even closer look revealed that the rear shock bolts had been installed backwards so the thick outer nuts were very close to the sprocket nuts. The shocks required removal and a 180 degree turn on the bottom to get the threaded portion of the lower clevis set properly, so the shock bolts, which have thin heads, were installed with them pointing outwards. The previous owner had commented that he had to put a longer chain on the bike to allow the rear wheel to be moved further back enough to clear interference with the forward edge of the rear fender, next to the swing arm. That sort of made sense, but then I discovered that the rear sprocket was stamped 32 instead of the stock 30 tooth markings. The stock 94 link chain had been included with the bike’s spare parts, but obviously wouldn’t work with the big tire combo.

I had brought a spare pair of new aftermarket chain adjusters to help brighten up the rear axle area, but one of then turned out to have stripped threads for the adjuster bolt. It is amazing how much time is spent sorting out all the little issues like these when you are wrenching on an older Honda bike with a little known history.

Once the rear wheel was reinstalled, it was time to move onto the front tire replacement. The first thing to notice was that the pinch bolt for the left front axle case was an Allen bolt, instead of the normal bolt with a 14mm head. Secondly, the bolt was loose in the threads. The bike had to be jacked up in front off of the starter motor, but the bike was also supported by a 2x4” board beneath the center stand feet to give the bike enough room to pull the over-sized front tire out of the forks and front fender. I had to remove one of the fender stay bolts to allow the wheel to clear the the fender’s cable stays. Apart from pinching the inner tube (there was a spare, thankfully), the front wheel went back together okay, except for installing a few front brake cable. The cable adjusters were mostly used up in getting the brake to adjust properly, which turned out not to be worn out brake shoes but the brake linkage arms had been installed one spline off from where the punch marks were shown. The wheels will be coming off again in the near future so the fenders can be removed and repainted, so the brake cam/arm issues can be addressed then.

The last few jobs for my 4-hour stint included an oil change, change the spark plugs and check the ignition timing. The first two tasks were easy enough but the last one brought a shock to me when the dyno cover was removed…

Instead of the typical CB72(L) rotor marks on the face of the rotor, I was faced with C72 marks which can only come with the use of a Dream or Type 2 engine CBCL engine. Beyond the surprise of seeing the wrong rotor installed, instead of a central rotor bolt to attach the rotor to the crankshaft there were two nuts, double-nutted on a stud! I have NEVER seen this adaptation done to a CB77 engine before or any other one, which leaves one to wonder, whether the end of the crankshaft threads were damaged previously and this was some kind of creative repair to keep the bike on the road.

The rotor had some black marker hash marks 180 degrees from the only stamped T and F marks on the rotor, which appeared to be properly set. I hooked up a dynamic timing light to the ignition and verifed the right side marks first. Then I used the black line mark as a hopefully accurate mark to set the left side ignition timing. The marks showed that the timing was retarded a few degrees, so a small adjustment was made to correct the error. The engine idles evenly and sounds like it has good compression. There are no signs of smoking, but there is no known history of what has been done to the engine beyond what has been discovered.

A quick ride around the neighborhood revealed that the transmission didn’t want to shift back into neutral when the bike was at a stop in gear. This is almost always due to someone removing the thin wire retainer rings from the clutch hub. The retainer wires help hold the first few clutch plates on the hub, which helps the rest of the clutch pack separate and release it’s grip on the transmission shafts. When the engine torque is removed from the transmission shafts, the shift selector can do its job of selecting whatever gear you wish, including neutral.

So, the next few upcoming hours will include removing the clutch cover, inspecting and cleaning the oil filter, checking what appear to be excessively strong clutch springs, looking for missing retainer springs and then popping in a new shift shaft seal while the cover is off.

If that doesn’t reduce the amount of clutch lever force currently experienced, then the kickstarter cover will be removed and a new clutch adjuster will be installed to reduce the amount of thread slack between the adjuster and clutch lifter arm threads. Reducing the slack translates into increasing the amount of clutch pushrod travel which separates the clutch pack more completely.

$100 worth of gaskets, seals, chain adjusters, clutch springs and a clutch adjuster have been lined up for the next round of repairs, hopefully the last for awhile.

Round Two….

The priority task was to address the clutch release issues, so the right side exhaust was removed to allow the kickstarter cover to be taken off to inspect the clutch adjuster threads/slack. Pulling and pushing the clutch lifter arm in and out of the clutch adjuster showed excessive slack/play between the two parts. The clutch adjusters are made of aluminum so the coarse threads are eventually worn down from repeated cycling of the clutch while riding. This bike was showing 10k miles and the parts looked original, so a fresh clutch adjuster was installed.

An unfortunate surprise when the kickstarter cover was pulled back was a splash of motor oil that had pooled below the crankshaft/starter clutch. Using a flashlight to check for oil trails, didn’t show anything that was really active on seals that were installed in the cases. So, that left the little seal that installs in the center of the starter clutch hub as the probable cause. Ordinarily, I would pull the rotor bolt and use the 16mm special tool to remove the rotor to check the starter clutch roller springs and the condition of the oil seal on the starter clutch hub. In this case, the C72 rotor that was looking back was being held in place by a stud and nut/washer instead of the normal rotor bolt/washer. As this was a house call visit, I didn’t have all the tools I needed to go further in this direction, so I had to wipe up the oil mess and leave it alone for the moment.

The new clutch adjuster was greased and installed, then the kickstarter cover reattached. Pulling the clutch lever felt about the same as before. So, the next step was to go to the left side, remove the exhaust system and footpeg/linkage to allow the clutch cover to be removed. The cover screws all came out easily and the cover came off with the gasket intact for a change. Pulling the clutch spring bolts out revealed what appeared to be the “white springs” which are stock for 305s of that time-frame. That was puzzling, but pulling the the plates off and looking carefully showed the probable cause of the clutch drag problems. I was somewhat surprised to see that the oft-removed steel retainer wires, which hold the first few plates in place, were still in place.

While the friction plates looked normal for used parts, the steel plates showed all the signs of an earlier “stuck clutch” condition where the plates had been pressed together for many years of storage, then adhered together transferring some of the friction material to the steel plates. It generally looks like a combination of rust and friction material that is left behind when the clutch is jarred loose by running the engine with the clutch lever pulled in until the clutch plates get unstuck.

When this approach is used, the leftover material on the steel plates keeps dragging against the adjacent plates which prevents a clean release of the clutch pack and causes difficulty in finding neutral when the bike is in gear and stopped at a light or stop sign. I had brought a set of steel plates that were NOS and rather than try to clean the old ones, we popped in the new set, reassembled the clutch plates and springs and then checked the clutch release function. You can watch the clutch separate by pulling the clutch lever in and kicking the engine over. When the clutch releases, you can see and feel the disconnect between the engine and transmission. It appeared to be working correctly, so we put it all back together again, refilled the crankcase and fired the engine back up again. Even driving the bike just a few yards in gear, then selecting neutral yielded the little red neutral light lighting up with ease.

So, the clutch release issues were finally solved and the bike is now driveable in traffic without struggling to get the transmission into neutral with relative ease. The total labor time ran close to 3 hours in wrangling all of the parts for the clutch release problem. That’s good news for now, but that oil leak is still present and will need to be addressed sooner than later. The owner wants to remedy the loose fork covers by replacing the little rubber ring packings that sit down inside the fork rings. That requires removal of the front wheel, fender, handlebars, fork bridge and all the related parts. So, that is the next round of labor to hopefully complete the major repairs and complaints for this 55 year-old classic Honda Super Hawk.

Round Three

This time, we had to resolve the mystery of the C72 rotor mounted on the end of the crankshaft with what appeared to be a stud instead of the conventional rotor bolt/washer that screws into the end of the crankshaft. I sourced a new CB72 rotor from my dwindling parts supplies, loaded it with new springs, caps and rollers ready to install, along with a seal kit to remedy the previously discovered oil leak issues. I brought a 3 jaw puller to attempt the rotor extraction and once it was in place, a few hard turns of the tool’s shaft brought satisfaction as the rotor flew off the end of the crankshaft, scattering little starter clutch springs, caps and rollers around the floor. With the rotor removed, you could see that the oil seal for the starter clutch hub was half-way falling out, which accounted for the oil leak. The main crankshaft seal seemed to be holding up okay, so we just replaced the clutch hub seal with a new one and reassembled everything with the new rotor. The mystery of the end of the crankshaft was resolved when it was revealed that a bolt had been welded into the end of the crankshaft! I guess no one will ever know why the previous owner took that path of repairs, but the end of the crankshaft still runs true, so it is what it is and it is good enough for the future.


Bill “MrHonda” Silver


Saturday, October 24, 2020

Honda… 1967

 American Honda was running into difficulties in 1967, at least with the US operations and sales. They had amassed a huge inventory of slow-selling models and financial challenges almost lead to their downfall in the American market. Honda’s engineers were also tasked with working on a new car line (N600-Z600 sedan/coupes) had just pulled out of Grand Prix motorcycle racing, and were diving into automobile GP racing, so resources were scattered out everywhere.

Honda had been selling basically the same motorcycles for 7 years, with few updates. The US line-up for 1967 was the whole line-up of now-obsolete push-rod-50cc Cubs (Honda went to OHC engines in 1965 with the S65), a transition from the CA95 to CA160, CB/CL160 twins, 250-305s and the blossoming CB450, which finally got a 5 speed transmission. Honda reportedly had imported 100,000 50cc Cubs during the early years. At $245 the Cubs few out of dealerships initially, but then languished as more powerful machines were offered.

While Honda continued to churn out old models, their rivals were gaining a big foothold in the US. Yamaha, Suzuki, Kawasaki and Bridgestone (which closed in 1971) all had innovative models, many with 5-speed transmissions and colorful paint schemes. The snappy performance of the 2-stroke engines gained many fans, especially due to their lightweight engines, which had few moving parts in comparison to Honda's more complex but sturdy four-stroke machines.

Seeing the handwriting on the wall, Honda began to move in the direction of cosmetic and mechanical upgrades to all of their models. Looking at the 250-305cc models, there were just a few visible changes, like alloy forks on the CB72-77s and restyled seats with upturned forward edges. Honda changed the transmission and crankshaft splines for easier manufacturing and added on some chrome fenders and an oval tail light to the Super Hawks.

Honda Dreams were mostly unchanged after the switch to “late style” models in 1963. Honda swapped out the old, tall, thin batteries for the short, fat CB77 batteries in 1966, which continued until the end of production. The oval tail lights are shown in the parts books for the 1967 models, but few have ever been seen in the US.

The buzzy Honda CL77 305 Scramblers had an engineering makeover, including the transmission splines and a rubber mount update for the seat, rear fender, muffler, fork ears and footpegs to improve rider comfort. The 1967 models also gained the “oval” tail light on the end of their production models, first on the standard silver-painted fenders, then with some late-release chrome fender models which also came out with the first of Honda’s Candy Blue/Candy Orange paint schemes.

There were other little detail changes like cleaned up carburetor bodies which had vestiges of never-used power jet casting features removed. The horns were changed to cheaper plastic versions and even the tappet covers had a different shape but never had a revised part number.

The “041” oval tail light assembly was sourced from a small C50 step-through model, but applied to all of the 1967 machines. For models like the SS125A-CL125A and the new 5-speed CL175K0, which were only sold for 3 years, the shape of the tail light defines whether the bike is a 1967-68 or 1969 which had a new taillight design featured on the CB750K0 machines.

For new models like the CB/CL350s and carryover CB/CL450s the tail light shapes were oval for 1968, then followed by the enlarged CB750 types.

One of the major changes for Honda in 1967 was the switch from JIS tread pitch to ISO standards. This changeover leads to many difficulties for models which were instituted before 1967 and continued afterward, like the S/CL90 models, CT90, and the CL1750K0. When looking at the microfiche parts illustrations and part numbers you see the transitions on fasteners and any other parts with threaded holes during the period.

The JIS to ISO changes affected 3,4,5 and 12 mm screws/bolts


3mm                                          0.6                     0.5

4mm                                          0.75                  0.7

5mm                                           0.9                  0.8

12mm                                         1.5                  1.25

The size of the bolt heads was also revised


3 mm                                      6 mm                  5.5 mm

4 mm                                      8 mm                  7 mm

5 mm                                      9 mm                  8 mm

6mm                                       10mm                  10mm

8 mm                                      14 mm                  12 mm

10mm                                      17mm                  14mm

12mm                                      19mm                  17mm

14mm                                      21mm                  19mm

16mm                                      23mm                  22mm

18mm                                      26mm                  24mm

20 mm                                     29 mm                 27 mm

All of these changes affected even the handlebar switch screws, as the transition continued. The rare NOS handlebar switches that come up for sale for most models, including the 250-305s all have JIS-threaded screw threads. Unfortunately, JIS threaded fasteners are quite hard to find anymore, so you are faced with having to re-thread JIS holes to ISO for these parts, as well as the 5mm screws on 250-305 point covers and dyno covers.

 Things began to start looking up in 1968, with the release of the all-new 350cc, 5-speed twins, the 5-speed 450s, and even the new CL175s now came with 5-speed transmissions. Most all 1968 models sported metallic paint schemes, more chrome and a new sense of purpose as they moved into the end of the 1960s.

Bill “MrHonda” Silver


Tuesday, August 18, 2020

Small part, big confusion…the 250-305 kickstarter pawl

 There are three little parts on the end of the kickstarter shafts of ALL 250-305cc twins from the 1960s. They are:

SPRING, PAWL product number: 28228-250-010

PAWL, SPINDLE product number: 28255-250-020

PIN, PAWL product number: 28256-250-000

Notice that the center codes of these parts is 250, which comes from the first generation dry-sump engines, which were built in 1957-60.

       Kickstarter shaft with kickstarter pawl and pin shown in correct installation order.

These parts are responsible for the kickstarter arm engaging the transmission’s low gear, which is connected to the crankshaft via the primary chain. While the kickstarter shaft only moves when the kickstarter lever is depressed, the kickstarter pawl/spring/pin parts are all actively engaged when the engine is running. The pawl is pressed into the inside features of the transmission low gear by the spring and pin, which stabilizes the spring as the assembly rides up and down inside the transmission gear.

For the kickstarter function to occur properly, several things have to be properly aligned and in good condition.

1. The low gear is supported on the kickstarter shaft by a stepped bronze bushing, commonly called the “low gear bushing.” This bushing is supporting two gears with a step in the middle to separate the two gears on the shaft. Over time, the bushing wears down, causing the low gear to wobble on the bushing. Also, the little step ridge on the center of the bushing gets worn down laterally, eventually wearing the ridge completely off of the center of the bushing surface. When this happens, the low gear is both wobbling on the bushing’s exterior and is also allowed to move laterally towards the adjacent gear and away from the kickstarter pawl.

2. The kickstarter pawl has a bit of “float” in the end of the kickstarter shaft, but needs to be fairly squared up inside the low gear’s inner engagement features. If the low gear gets too cockeyed and wobbly on the bushing and kickstarter shaft end, then the kickstarter pawl can’t fully engage the inside of the low gear and the whole mechanism “slips,” instead of engaging the engine properly.

3. Because the kickstarter pawl is always engaged, operating basically as a one-way clutch, the edges of the hardened steel pawl eventually wear down, causing another reason to create slippage when you try to kickstart the engine. The little pawl pin pushes up on the back side of the pawl to keep it engaged with the low gear teeth. The pin is spring-loaded by a tiny coil spring that drops down into the hole in the end of the kickstarter shaft. After many millions of cycles of up and down for all three parts, they eventually wear out. The sides of the spring can wear flat and begin to grab the outside of the pawl pin and the two begin to accelerate wear together, as they do their best to support the pawl itself. The tip of the rounded pin begins to flatten out, as well. In high-miles engines, the “teeth” that engage the kickstarter pawl on the inside of the gear also wear down, so they can’t hold the pawl end properly.

4. When maintenance is left undone, due to lack of oil changes, poor engine tuning and other factors that put additional stress on the kickstarter pawl system, eventually it fails completely. Because these parts are part of the transmission, the engine cases have to be split in order to replace the worn and damaged components. In some cases, either the end of the kickstarter spindle that supports the pawl will break off and/or the roller bearings that support the transmission gear on the opposite end of the shaft will wear through the hardness of the shaft surface and begin to dig into the shaft. 

Instead of rolling smoothly, the transmission gears start to engage the shaft during on-off throttle conditions. What happens is that the kickstarter shaft begins to swing back and forth, while the bike is being ridden. On a CB72-77, the kickstarter arm can come into contact with the rider’s shins on the right side, in a surprising display of force, as the kickstarter arm goes forward on its own, then whips backward towards your leg.

5. Another wear point in the transmission, being affected by the kickstarter pawl is the 14mm end spindle bushing surface face. The continuous movement of the pawl pushes up against the edges of the 14mm bushing causing the pawl to dig a trench into the bushing face. This adds more end play to the already sloppy transmission gears/shafts and can cause the gear dogs to lose their engagement contact surfaces. When this happens, the transmission jumps out of gear and when this repeatedly happens, the transmission gear dogs get rounded off causing even more shifting difficulties and damage to the transmission components.

In more than a few cases, while doing repairs on used 250-305 transmissions, has lead me to discover that a previous repair attempt has left the kickstarter pawl improperly installed. On a recent CL77 transmission repair, the bottom end, which had been apart twice, had the pawl installed backwards, so that the sharp edges were engaging low gear, just barely. It was “working” to a degree, but obviously it wouldn’t have lasted for a lot longer. The owner reports that the transmission repairs, including offset cotters, now shifts very smoothly and the kickstarter works perfectly.

                                             Incorrectly installed kickstarter pawl!

Bill “MrHonda” Silver


Image credits to and Cappellini Moto (spindle bushing), eBay sellers and MrHonda.

Friday, August 14, 2020

Adjusting to the modern world…. Re-jetting vintage Honda carburetors

 For those of us who were alive and involved with 1960-80s Honda motorcycles before the advent of “unleaded gas” and “10% alcohol gasoline,” we remember that Honda motorcycles were carefully jetted for maximum power, economy and reliability, right out of the crate.

                                            Honda CB72 carburetor with "power jet" function.

Reviving those 40-60 year-old motorcycles generally requires fuel system cleaning and a careful inspection of the carburetors. Before the introduction of CV (constant velocity) carburetors on the DOHC CB/CL450 twins, the vast majority of Honda’s carburetors were made by Keihin and were simple throttle-valve units, consisting of a float valve, float, main jet, idle jet, carburetor slide and tapered slide needle. Changing the fuel calibration of the basic designs to accommodate various versions of each application was generally required when the exhaust systems were changed from CB=Street to CL=Scrambler. With mostly identical engine specifications between two series of machines, the change from a low-mount to high-mount exhaust causes the carburetors to act differently and so Honda’s engineers carefully made appropriate changes to needle taper, main jet and sometimes the idle jets to bring a smooth fuel delivery to each application.

For the most part, Honda offered many sizes of main jets, idle jets and needles to re-calibrate the carburetors, as needed. In the early 1960s, Honda changed the basic shape of the float bowl from a rounded shape to one that was more squared-off on all sides. There was no need to change the calibrations as the body shapes changed. When owners began to alter either the intake or exhaust system for more “performance” the original calibrations are no longer valid. Changes to the intake or exhaust systems often require a change in the jetting of the carburetors due to an increase in airflow or alterations in the intake or exhaust tract length. Changing the tract lengths changes the resonant frequencies of the systems which can enhance or detract performance from the original settings.

For example, the difference between the 305 Honda Super Hawks and Scramblers lie in both the exhaust header pipe lengths, muffler lengths and the length of the intake to air cleaner runners. The engines have the same pistons, cam timing, valve sizes and carburetor bodies, but the standard main jet of a CB77 is #135 while a CL77 runs jets down around #130. Even the pilot jet sizes change from #38 to #42 between the two models. 

The Scrambler’s long, long, header pipes have a much different resonance frequency that bounces a pressure wave back to the exhaust port that can affect the incoming intake charge in the cylinder. The longer intake and exhaust tracts of the Scrambler enhances some of the mid-range torque, while the shorter CB intake and exhaust lengths enhance higher rpm performance on the road or race-track. Scramblers are geared shorter than CBs, so feel “more powerful” than Super Hawks, but the CB77s will hit nearly 100 mph vs about 85 mph max on a Scrambler. While 305 carburetors with 26mm slides have 2.0mm cutaways, the CL72s have a 3.0mm cutaway but the CB72, with the same-sized carburetor has a 2.0mm cutaway. You have to look over each item carefully, if you are tempted to start mixing and matching Keihin carburetor parts from similar models.

Be aware that prior to 1967 all of the Honda carburetor jets were JIS thread pitch and thus not interchangeable with later ones. Main jets in ISO dimensions have a ring marked around the outside edge of the jet, whereas the JIS threaded jets were left plain. This can cause great confusion when you have a model like the 1965-69 S90, CL90, SL90 models. which bridged the 1967 changeover gap. When people start trying to mix-match a box of loose parts from models like these, problems will arise.

Fast-forward to the 21st Century and most all markets have succumbed to at least 10% alcohol-infused gasoline which is fairly unstable in long-term storage and has less fuel energy that pure gasoline. In order to compensate for the loss of fuel energy (and a slightly different fuel viscosity), the rule has become that bumping the carburetor main jets up at least one size (5 to 10%) will equalize the air-fuel ratios that these old engines were used to seeing. After setting up stock CB77 Super Hawks to original stock settings of #42/135, I found the bikes to having flat spots and seemed to be struggling at highway speeds. Swapping the #135 main jet for a #140 pretty much cured the mid-range/top end power problems and even helped the normally cold-blooded Super Hawks to warm up quicker and have better overall throttle control.

Similarly, I have had to re-jet a number of CB400F Super Sport fours from #75 to #80 main jets, in order to overcome the same lean conditions. I made that change to a bike that I sold to a young man from NY. He flew in to San Diego and drove the newly rebuilt machine all the way back to NYC in 4 days, running it at 70-80 mph for most of the trip. When I first drove the bike, after a careful check over (and it had an electronic ignition), the bike struggled at freeway speeds, feeling flat and struggling. A simple step up in the main jets solved the problem and allowed a successful cross-country journey, which I think might have suffered a melt-down due to the original lean jetting coupled with alcohol gasoline.

Bear in mind that by the mid-1970s, the EPA was beginning to lean on motorcycle manufacturers for their part in the increases of carbon monoxide and hydrocarbon that the world was experiencing. Motorcycles were carefully calibrated for emissions during start-up, idling, off-idle performance and at full throttle, just enough to keep them from seizing their air-cooled pistons during extended riding conditions. I think we have all seen the idle mixture screw limiters that were required to keep owner’s from destabilizing the factory settings. Lean mixtures due to slide needle taper designs were another part of the equation and soon owners were putting little thin shims beneath the needle heads to raise them up slightly to enrichen the fuel ratio mixtures at part-throttle.

1980s Kawasaki motorcycles were famous for requiring 5-minute warm-ups, just to get the bikes down the driveway due to lean idle/part throttle calibrations required to keep the engines clean enough to pass the EPA regulations. Kawasaki was always pushing the envelope on performance machines, but the more power they make, generally, the more pollution is created in the process.

In order to enhance engine performance, companies like “Dyna-Jet” began to develop “Stage” kits to help owners get a handle on carburetor calibration issues with either bone-stock machines or for ones that had a 4:1 aftermarket exhaust or replacement air cleaner element or full system. These were sold under the guise of being a “racing” product that was not to be installed in production street bikes, especially in strict-California emissions zones. Dyno tests generally showed some improvements to horsepower, throttle response, torque readings and overall drive-ability with installation of the kits, but obviously the previous emission calibrations were out the window and any measured emissions were substantially higher than those that were create at the factories.

The days of carburetors are numbered due to the introduction of efficient fuel-injection systems and computer-controlled ignition advance curves. But in the meantime, we have to do our best to work with what we were dealt with from the factories dating back sixty years. So, to begin with, we have to clean, clean, clean the carburetor bodies and all associated components, then start to make educated guesses about what the engine will need in the way of corrected fuel-air ratios at all engine speeds and conditions.

Just assume that the use of alcohol-gas is going to make the engine run lean with stock OEM jetting settings. Once the fuel passages are all clean (ultra-sonic cleaners are great!), then a careful look at each internal component is next and then consider obtaining some slightly larger sized main jets to begin the calibration experimentation. Multiple test rides will give you a “seat of your pants” feel of what the bike is trying to do and what it wants in the way of fuel needs. When you feel the flat-spot or performance plateau/misfire, try to pull the choke up slightly to see if the problem gets better or worse. If it improves, you need to richen up the mixture. If it gets worse, lean it out again.

Reading spark plugs is somewhat of a black art, as well, but an initial look at the overall appearance of the plug tip will tell you if it is running lean (all white tip), rich (black and sooty), fuel/oil-fouling (wet end) or has a nice tan insulator without a lot of build-up of carbon or oil.

The bike should start up with sometimes full choke for just a moment until it is running, then reduce choke to around 1/2-3/4 while the engine warms up. Backfiring back through the carburetors/air filters is a sign of a too-lean fuel condition. If the bike fires up with no choke, it is generally running too rich at idle and off-throttle. The engine should idle down normally after about 4-5 minutes of operation time and the air-mixture screws should cause the engine to change idle speed and quality when they are turned in and out within a quarter-turn of normal. Always make the final idle mixture adjustments when the engine is at full operating temperature.

If the idle mixture screws are not responsive, then you have issues with jet sizes, blocked air/fuel passages inside the carburetor body, air leaks at the intake manifolds or warped carburetor bodies at the flanges. Ensure that the suggested float levels are use without fudging more than a millimeter or so. If you have fuel running out of the bowl’s overflow tube, you either have a float valve not sealing, a float level that is too high or a crack in the brass tubing of the bowl overflow tube.

While Honda bolted carburetors directly onto the cylinder heads in the early years, they began to recognize the high-frequency engine vibrations could cause fuel frothing and inaccurate metering at various engine speeds. The new-generation 350s and 450s used rubber-fused manifolds to secure the carburetors to the engines with both damping qualities of the rubber, as well as some heat insulation features which helps to stabilize metering in both hot and cold driving conditions.

As an example: The little 1960s Honda 160-175 twins had solid-mounted carburetors, bolted to aluminum intake runners, which were then insulated from the head with phonolic blocks and o-rings. But, when Honda revised the 175 twin engine up to 200cc in the early 1970s, they created rubber intake manifolds to improve fuel metering and vibration dampening of the carburetor bodies.

Some of the most confusing carburetor sets are featured on Honda CB/CL350 twins. There were several different carburetor body styles and 4-5 different calibrations suggested for the bikes, depending upon whether they were CB or CL versions (and the early SL350s, too). In the case of the 350s, there were different camshaft timing periods between CB and CLs, so that, alone, is enough to cause changes in calibration settings. These early CV carburetors featured both a primary and secondary main jet to help with the transitions from part throttle to full throttle conditions. Sometimes, all the changes needed were to bump up the primary main jet to the next size in order to smooth out the throttle response. One of the problems with 350 twins is that they vibrate quite a lot and the original mufflers for both CB and CLs tended to either break or rot out prematurely. Replacing the damaged components with OEM items (of which there were several types) was often costly and the parts were hard to find due to demand. Owners resorted to use of other slip-on muffler systems which had different lengths and back pressure features, all of which caused metering problems back at the carburetors.

Many of us “old-timers” know that the carburetors are the LAST thing to blame/adjust when engine performance is suffering. Setting up carburetors to operate correctly requires a sound foundation in several aspects of the engine’s systems. Go back to the beginning: Compression test, valve adjustment, camchain adjustment, ignition timing settings, spark advancer function, coil/condenser/point conditions, spark plug caps and even the correct spark plugs are all to be checked and confirmed before diving into the carburetors.

If you have a low-compression engine that is using oil and fouling spark plugs, the carburetors probably are not the root cause of your engine performance issues. If the point contact faces are all pitted due to age/miles or a bad condenser, you will have erratic ignition output at the coils. If the coil leads are crispy and cracked, the sparks might be jumping to somewhere else than the gaps of the spark plugs. Spark plug caps should have no more than 5k ohm resistance measurements and should be screwed onto the spark plug wire ends which have been trimmed back to bare wire.

Aged condensers cause points to arc randomly or excessively which adversely affects ignition coil output. Make sure that you are using a fully-charged, load-tested battery and that the charging system output is keeping the battery charged during operation. Engine vibrations can cause loose connections in the wiring harness and individual connectors to loosen or disconnect altogether. When Honda started putting ignition switches up in the center of the fork bridge, the pull on the switch connector often causes the switch connection to come apart, partially or completely. Bikes with KILL switches need to have the switch contacts checked and the wire connections secured so the coils get a steady feed of voltage.

All of these aspects of motorcycle function and maintenance can come into play causing performance issues that are first attributed to “the carburetors.” Obviously, if the carburetors have been sitting for months/years with old fuels in the bowls, then they need careful cleaning and scrutiny for normal function. Carburetor work is made more difficult with the alcohol in the fuel, which attacks most rubber parts, especially float bowl gaskets! If you drop the bowl off of a carburetor and the gasket is not the original glued-on version, chances are that the gasket will swell up and will NOT fit back into the carburetor body grooves. Cleaning with soap and water then drying in the sun or gently with a heat gun will generally allow them to reclaim their original shape and size. If you are doing a lot of jetting or carb work, plan on getting several sets of bowl gaskets to have on hand for quicker service procedures. 

To review:

Test drive evaluation…

First, start the engine and listen to it to hear if it is going to need a prolonged period of “warm-up” or if it will take enough throttle to drive off after a minute or two of running. Run the bike up gently with slowly increasing throttle openings. Listen and feel if the engine is taking throttle cleanly or if there is a hesitation or misfire occurring at certain throttle openings. While driving, if it is safe and easily accessible, pull up the choke lever or knob slightly during the time when the misfire or roughness is occurring. If you feel a surge of power or increased smoothness in the engine performance, then you will need to enrichen the fuel mixture at that point.

Off-idle hesitations can be resolved with either an increase in the size of the idle mixture jet and/or raising the needle slightly with shims. If the hesitation is more in the ¼ to ½ throttle settings, then you can raise the needle a little bit more and/or increase the main jet size slightly, one step at a time. Remember that if you increase the main jet size, you have enriched the whole fuel ratio from around ¼ throttle all the way up to WOT. If you get a good full-throttle response, but the mid-range is sagging and the plugs start looking dark and sooty, start to lower the needle back down one step at a time.

It’s a balancing act, but one well worth pursuing in order to maximize the engine’s performance over a wide rpm band and to conserve fuel that might be wasted in an engine that is running excessively rich. Pull a spark plug or two and look at the tip to see if they are getting a nice color on the ends which indicates proper jetting.

Excessive rich conditions can wash down the oil on the cylinder walls, leading to ring wear or even piston seizures in extreme cases. Excess fuel will contaminate the engine oil, as well, leading to lubrication breakdown. There is a whole chain of events that happen when you start to “adjust” the carburetor settings, so think it through first, before you begin wholesale changes. On many bikes, just removing the carburetors is a huge pain, so you don’t want to be in the position of having to do it more than once or twice, at the most.

Take time to understand each stage/function of a carburetor, so any changes you make are done with caution and thoughtfulness about what you are trying to achieve. Carburetor wizards are getting harder and harder to find these days, now that fuel injection is becoming more and more common. Take time to learn the craft for yourself and to help your friends who are in need of timely and educated repairs.

Bill “MrHonda” Silver


Friday, August 7, 2020

1964 CL72… ornery and out of the ordinary

Lately, I have been nursing a somewhat one-off 1964 CL72 250cc Scrambler, for a new customer who has owned it for many years. His family owned a Honda shop in the Mid-West and this bike has stayed in the family for a long time.

I had been contacted by the owner to “get it running” after it had been stored for a long time. It seemed like a fairly simple request, but I haven’t worked on a 250 Scrambler for quite a while and had forgotten how difficult they are to do simple maintenance on without having to disassemble half of the bike every time you need to service the carburetors.

What’s special about this bike is that it had been built with Akront alloy rims, over-sized tires and a CB72-77 cylinder head, featuring a tach drive. A later model CB77 speedometer and headlight shell were installed in place of the usual single meter setup. Additionally, the bike had been fitted with a YL72 alloy fuel tank, which was a factory-issued “racing part.” These tanks are very rare and made of an easily damage alloy, so finding ones in good condition is a rare event, 56 years after production.

I gingerly removed the fuel tank after working off the old fuel lines and set it aside for petcock repairs. Also, the original gas cap latch for the “flip cap” filler had broken and somewhere along the line the owner’s father had contacted me about some billet ones that I have made available for the past 10 years. The problem was that the retainer pin had been removed/lost and so a beach-ball inflator had been inserted into the cap latch pin hole, as a temporary fix. Additionally, the caps had a cork gasket installed to seal the opening and the cork had broken up so a 329 code Honda gas cap gasket was installed around the central holder. The OD of the gasket was too small, so the cap leaked during driving.

When the tappet covers were removed for a valve clearance check, I was greeted with the look of alloy valve spring retainers, so I could only imagine what had been done to the engine beyond that. The clearances were close to stock .004” so I just reset them all to that, hoping that the camshaft was still a stock unit. The carburetors and air filters were removed for cleaning (filters replaced) and that gave easy access to the camchain tensioner adjustment nut/bolt. The adjuster moved in about an eighth of an inch, so you can either assume damage to the roller or just a lack of maintenance of the tensioner.

The clutch pull effort was very heavy, leading me to think that there was some kind of heavy-duty clutch installed, perhaps with the 275-810 clutch springs from the CB77s. After draining the dirty oil and removing the clutch cover, the clutch pack was removed. It was apparent that the clutch was a Barnett performance unit, including the springs. The clutch plates were stuck together and the wire retainers for the clutch hub were missing. Fortunately, the clutch plates were of the correct thickness so that the wire retainers could be installed, making for a clean clutch release action for city driving.

With the clutch cover removed, the oil filter was accessed, which proved to be packed with an eighth inch of dirt/crud. The filter was cleaned and reinstalled. This bike had the “small hole” clutch cover, which barely clears the OD of the filter, so doing a filter service with the clutch cover in place is impossible. Overall, the insides looked fairly clean, so the cover was replaced. In order to minimize the clutch pull effort, the kickstarter cover was removed for replacement of the clutch adjuster. The clutch adjusters are made of a soft material and wear down quickly, especially if not kept lubed up and when asked to work against heavy-duty clutch springs.

The carburetors were removed, disassembled and cleaned in a sonic cleaner, then reassembled with new bowl gaskets and o-rings; the rest of the parts were reused. The petcock was rebuilt with an aftermarket kit and all was put back on the bike for an initial fire-up. Well… The petcock fuel lever was pitted on the back side, so it was dressed up with a file, which took out most of the imperfections. Even after a couple of rechecks, it continued to slowly drip, drip, drip… When the carburetor fuel lines were attached, the float bowls began to weep around the forward straight edges of the bowls. This has become quite a problem for me lately. Part of the problem is that the non-OEM gaskets are a little too wide where they encounter the locating posts. The gasket channel is about 3.25mm and the gaskets are 3.5mm wide. When installed the gasket tips up against the posts and doesn’t lay flat into the channel. Installing the bowl should, theoretically, just clamp down on the gasket and flatten it into the channel.

Most of the aftermarket gaskets are layered instead of solid material and it may be that the gasoline is bleeding through the material. Even rechecking the float levels several times, the bowls continued to weep a bit. I dug out a solid rubber gasket from an old kit and installed it in the left side carburetor, which seemed to have solved the problem, but I only had one to use. The bike came with a box of odd spares including a set of 1967 CB77 carb bodies. I took the bowl clip off of one of the spares and tried it on the CL72 carburetor after I had notched the gasket with a small paper punch. That seemed to work, but overnight there were signs of fuel leaking and it turned out to have a tiny crack in the overflow tube. A spare bowl was installed and that seemed to be the cure.

With everything installed, it was time for a road test. Initially, the bike fired up loudly (straight pipes with no baffles) and it seemed more or less okay. When I took off, in gear, the engine bogged down, then cleared itself after about 3k rpms. Above those engine speeds it seemed to run strong, but cracking the throttle in low gear at slow speeds repeated the bogging down feeling. Because it was jetted for 1964 fuel (no alcohol and lead added), I have generally found that the carburetors need to be jetted up to compensate for the 10% alcohol in the gas. Removing the float bowls, in order to change the main jets, set up another challenge… the float bowl gaskets fall down and absorb the alcohol in the gasoline, causing them to swell up and then they don’t fit back into the carburetor bodies!

I have found that taking the gaskets out and laying them in the direct sun for an hour generally dries out the gasoline and the gaskets shrink back to size again. I reinstalled the new main jets, after I had raised the needles one notch and put it back together again. Now it wouldn’t even run on the right side cylinder! At first, there was no power to the points on that side. Removing the seat and then the tank bolt gave enough room to access the wiring connectors to the coils. One connector was snapped in, but you could feel that it was dancing around inside the connector. A squeeze with some pliers and a good push in remedied the power problem to the points. I dropped the tank back down on the mounts and tried to start the engine again… STILL not running, but on the left side now. I raised the fuel tank back up and got the bowl off from below the carbs. There is VERY LITTLE room to do carburetor work on the left side with the carbs still mounted on the engine. The float valve needle turned out to be rubber-tipped, and it jammed itself into the float valve seat, shutting off the fuel supply to the carburetor bowl.

I dug out an all-metal float needle and installed it while the carb was still attached and shrouded by the exhaust pipes and the dipstick tube. This really takes watchmaker skills to do and it doesn’t go easy if you are successful. Of course, the float bowl gasket had dropped out of the body, so that was the second step to accomplish. Eventually, everything was back in place with larger main jets and needles raised up. The result was pretty much the same as before. It still has a big bog off-idle, then clears up and runs well at high rpms. Pulling the choke on when it was struggling just made it worse, so apparently, we have to go the other way with the needles and see if that helps, even though it is counter-intuitive to what is generally found when jetting vintage Hondas.

Potential factors in why it is running the way that it does are: Straight pipes with no baffles installed. The pressure waves from the long pipes may be out of synch with the carburetor calibrations causing an over-rich condition. Secondly, if the cam was changed, along with the valve springs/retainers, the cam timing may be causing low-speed running issues and/or both factors could be at play.

The throttle cable on the bike was very old and coming apart at the ends. I decided to stop playing with it until a new cable comes in and then I can drop the needles back down at the same time. Other tasks done on the bike included painting the aftermarket chain guard and making repairs to the gas cap.

The bike barely stood on its centerstand because there as an ancient 4.00x19” tire mounted on the back and a 3.50x19 tire on the front wheel. Several hundred dollars later, a stock-sized set of Metzler tires were mounted up, but the bike is still a little unstable on the centerstand because the aftermarket rear shocks are about 1/4” longer than stock.

Much of the wiring harness was replaced, previously. The neutral light bulb was broken when inspected, but a new one didn’t light up apparently due to a neutral switch malfunction, which is located beneath the kickstarter cover. In order to remove the clutch cover or kickstarter cover, the footpegs must be unbolted from the bottom of the frame. There are few straightforward repairs or adjustments that can be made on a 250-305 Scrambler, without having to remove 3-4 associated parts in order to gain access to what you wanted to do in the first place.

Of all the 250-305 models, I have found the Scramblers to be the hardest to work on and the least satisfying to ride once you finally get them going properly. Because of the closed-loop frame and the exhaust system bolted to the side of the chassis, the amount of vibration becomes excessive and fatiguing, at least to me. For the die-hards who think that Scramblers look cool and sound cool, they can have their say, but they will not sway my opinion of them in the least. Give me a nice Super Hawk any day!

Bill "MrHonda" Silver 07/2020