MrHonda vs the unruly 1964 250 Scrambler

 The recent acquisition of a sad-looking CL72 lead me down the path of the usual revival techniques, including a new battery, fuel system clean out (tank, carbs and petcock), plus a fresh set of tires and cables.

The carbs were pretty gummy and I tossed the bits into my ultrasonic cleaner for several rounds. There was some residual corrosion and grime in the nooks and crannies, but the bike had been running on them previously, I assumed.

    

CL72 carb specs are #115 main jets, #40 idle jets and a 26.5mm float level. Pretty straightforward, huh? I mounted the carbs on the bike w/o air filters just to get it running and see if the 150/60 psi compression readings would change with a bit of run time. After checking the ignition timing and valve clearances, I hooked up the carbs to a remote fuel bottle and cranked it up. It wanted full choke at first, but settled into a steady idle rhythm with no unusual noises. After about 10 minutes of running, the compression on the low 60 psi side came back up to match the 150 psi on the high side. Things were seemingly looking promising for a quick turnaround for this 62 year-old machine.

I had sealed the fuel tank and rebuilt the petcock, so it was all installed with the seat for a short test ride. Nursing it down the driveway and around the block revealed what seemed to be a big lean flat spot just off idle and an attempt to catch on at higher revs. I limped it home and started troubleshooting.

The aftermarket points and condenser set installed showed running point gaps at .14” and .018” with the backing plate centered on the adjustment slots. Reducing the point gap increases the coil dwell time, but the geometry of the aftermarket points was just off enough not to allow any meaningful adjustments. This was yet another example of the failings of non-OEM point sets on vintage Hondas.

/I had one of the last Pro-Trigger e-ignitions on hand, so decided to install it on this bike to ease the timing woes. Starting the engine up again had no effect on this sudden massive flat spot in the throttle settings. So, onto the carb settings again. I hadn’t removed or checked the main jets in the holders and discovered that the jets were #125! This was puzzling as they were 10 numbers larger than stock. I had accessed a new set of OEM needles which were set at the middle adjustment notch initially. I dug out a set of #115s and installed them, but the flat spot just got worse. It wouldn’t keep running off a nearly full choke condition.

I removed the carbs once again, rechecking all the passages and deciding to change back to the #125s and raised the needles all the way up. Once installed the engine began to show signs of normal life, but not a lot of clean throttle response. I turned back to the ignition system for checks.

In installing the E-ignition system, I removed the spark plug wires from the coil and discovered that the plug wire was not fully engaged into the central spike. The cavity was rusty and corroded so I cleaned out the plug wire hole, but then discovered that someone had connected the coil polarity backwards! I had some spare used coils, so started to check them against the installed ones. I discovered that the secondary resistance readings were 14k ohms on one coil but about 8k ohms on the other five so chose a set of those. I transferred the wire connections to the new set of coils and cut back the ends of the wires to ensure that there was clean wire strands to engage with the central spike. I discovered that the old wire end was not fully pressed into the coil housing, so that was remedied.

It seemed like one cylinder wasn’t firing as well as the other. Checking for spark on a plug grounded to the head, had one side visibly reduced in spark at the gap. I checked the NGK plug caps for resistance problems but they both were reading about 4 ohms. I screwed another fresh cap on the wire and it seemed to get a better spark.

The tank and seat were on and off the bike a half dozen times for test rides that continued to improve, but not achieve a normal function. One problem is that the original fuel tank was replaced with a 1967 tank which does not have a crossover tube function. When fuel runs low on the petcock side, there is still some fuel in the other side of the tank that is inaccessible. One test ride left me feeling that it was running on one side and when I nursed it back home the right side bowl was nearly empty. This brings up another phenomena of Honda twins with duel feed lines coming from the petcock. There are times when the petcock only feeds one carburetor, despite the fact that both lines are the same length and fuel source is sufficient. You can check it sometimes by pulling a fuel line off the petcock and nothing comes out until you plug the petcock fitting with your finger for a moment, then suddenly the fuel begins to flow once again.

There is some kind of fluid dynamics issue going on there, that is not easily understood. If one carb gets filled before the other, then when the line if full, the fuel should transfer to the other port. Perhaps an air lock occurs in the empty line that needs to be bled out to encourage fuel flow once again.

At any rate, the last test ride yielded better running results with the #125 main jets and needles all the way up, however a plug check showed the left side running too rich off the needle setting whereas the right side plug came up clean. I dropped the needle on the left side down to the middle notch and restarted the engine to ensure that it was improving on the left side.

Now that the bike was almost ride-able a new issue of concern arose. Initially, the clutch feel was normal and the bike dropped into gear without the big bang when the plates are stuck together. The bike had been sitting for about six years, so the stuck clutch symptom is not unexpected. However, when I was shifting at low speeds the transmission began to jump in and out of gear while riding, and then it became increasingly difficult to find neutral. Sometimes the light would come on and it was still in gear, all of which leads me to the conclusion that the dreaded engine pull is required to sort out the clutch and transmission woes. This becomes an all day event of removing, disassembling, repairing and reassembling the engine again, then the reinstall into the chassis. These are the reasons why the CL72-77s bikes are not high on my list for repairs and overhauls.

FYI, even if you know what you are doing, a transmission job on a Scrambler is around 6 hours, plus parts. I pulled the engine out, reluctantly, then had to pound away at most all of the screws, then discovered that the clutch cover gasket had been glued on with Honda Bond sealer. The second gear dogs were rounded off and barely had any overlap, which was the cause of the gear jumping. The center ridge on the low gear bushing was rounded down leaving a tiny worn-off ring lodged inside the low gear opening.

I have a number of transmissions from later-model engines, which use the back-cut gear dogs and better gear dog overlap to begin with. The low gear bushing was replaced and almost an hour spent removing the old factory sealant between the cases and then slowly scraping off the clutch cover gasket residues. The clutch plates were replaced with what looks like Barnett clutch discs, but the hub was the original version with 3 retainer wire grooves, but no retainer wires. I re-drilled the hub to secure the first plate and added the vented outer cover. In cleaning the clutch cover I discovered some grooves in the top of the cover where the old primary chain was rubbing up against it, perhaps during the Jumping of the Gears experience. Reluctantly, I installed one of my few remaining new primary chains to ensure that the engine would have a long life. I buttoned up the engine and installed it into the frame. Done for the day. Will finish up in a day or so, then move on to the other projects that are remaining in the shop.

Wrapping up the engine repairs and installation, more problems arose, partly from my lack of care on the assembly of the engine’s bottom end. When the kickstarter cover was installed and the clutch adjuster turned near the index marks, the clutch cable was limp when I pulled in the lever. I started the engine and tried to put it in gear, but it stalled immediately. I first assigned the clutch adjuster misalignment to an extra steel plate installed so the outer clutch plate would just engage with the plate stack. First I double checked the kickstarter cover to see if the steel ball had fallen out. It was still in place, so that left pulling the clutch cover to see what was going on inside.

With the cover off, several things stood out as problem areas. First, the used snap ring that holds the inner clutch hub in place had dislodged, disconnecting the clutch function altogether. I new snap ring was installed and the clutch stack reassembled. When the engine is assembled with the kickstarter cover, you can see how adding or subtracting a plate affects the position of the clutch liver and the clutch adjuster alignment marks. In this case, I removed the extra plate and the marks came closer to alignment, plus the clutch lifter was functioning more normally, arcing through a smooth path when the clutch lever was pulled. As I started to install the oil filter, I noticed that the sprocket was spinning on the crankshaft end! If you are not careful with the conical washer staying in place when tightening down the crankshaft nut, the parts will not stack up correctly and the sprocket fails to spin the oil filter. So, it was a 3 in 1 followup repair, now fully functional again. The third and forth days were devoted to engine removal, repair and re-installation. Final tuning is the last step.

It was still hard to start with the choke, so I opened it fully with the engine still cold and with part throttle, it fired up and caught revs almost normally. I let it warm up then tried the quick around the block test and noticed that the part throttle flat spot was still somewhat present, but once the revs got up around half throttle, it pulled with some authority. I tried a longer half mile downhill/uphill test run and the bike accelerated cleanly with a big handful of throttle, but was still a little lazy off idle. The carb needles are still in #3 slot and the main jets are still #125. After a little cool-down, the plugs came out looking white, giving the indication that the bike was still running somewhat lean, although the sound of the engine seemed to be running perhaps rich at part throttle. At this point, it is trial and error until the end result is a smooth engine take-up from idle towards mid-range and beyond. Ultimately, the final combination was #120 main jets and the needles all the way up. I must have had the tank and seat on and off more than a dozen times, trying to eliminate problem areas and do more diagnostic work to find the causes of poor running episodes.

I spent the better part of 4 days, trying to noodle out the reasons for the sudden engine mis-behaviors and had only gotten about 90% of the issues solved. Make a change, try it out. Make another change, try it out…. It ain’t easy being MrHonda sometimes. I’ve never run across a 250-305 that has defied so many attempts to resolve the running issues. When everything is “correct” as far as compression, ignition timing, carb settings and ignition component conditions, it should run as normal.. sometimes that is not the case.

Bill Silver

aka MrHonda

www.vintagehonda.com

Reunion: Fraternal twins separated at birth. 1969 CB175s

 Well, it is another crazy referral to my already busy schedule of repairs and restorations, but SOMEBODY has to do it. This time, I received a text message saying that a young guy had purchased a set of 1968 CB175 twins, both with low miles, but had been sitting for almost 30 years. The warehouse photos looked promising, but the reality was less than impressive.

                                                    #1 DONE 3/27/26

The fragile side covers exploded when they were pried out of the hardened rubber grommets. I had to use a heat gun on the carb bodies to soften up the old gasoline varnish residue. The forks started leaking as soon as the bike was sitting on the side stand. The air filters were all clogged up and in doing research the air filters and covers had a part change in the 4k range, but this bike is 3130. Exact details are difficult to discover with current part number listings. All the control cables were frozen or seized up. The clutch is of particular concern, as it will require draining the oil and diving into the clutch assembly, then scraping the gaskets and reassembling it all.

The front brake cable, which has the front brake light switch embedded, didn’t move an inch until I disconnected it. The brake cams on the brake panel were seized solid. The throttle cable, was of course, frozen due to the slides which were glued into the carb body bores by old gasoline varnish gum. The original tires were badly cracked all the way around on both sides. The left side of the handlebars was bent up and kinked at the bend. When I put an old fork tube on the end to pull it back down, the tubing split open at the bend site. I wrangled with an eBay seller in RI who had a straight and somewhat clean set of OEM handlebars for $70.

The drive chain was rusty, of course, as were all the turn signal stalks and lens units. Rust was the general theme over the entire motorcycle. Both fenders and the tail light bracket were all pitted. The headlight rim screws were very tough to remove, as the ends were rusted where they extended into the headlight shell.

Once the carbs were removed, I pulled the spark plugs for a compression check. Happily, the readings came out in the 130 psi range, which should be good enough to make it run. The carbs were carefully dismantled and bathed in the ultrasonic cleaner for about a half hour. New kits are coming in with the other $400 parts order from 4into1.com I did find a new pair of $100 air filters from DavidSilverSpares.com, here in the US, fortunately.

I spent a half hour removing the front brake panel from the cable and the front wheel, then dismantled it to clean the brake cams and scuff up the asbestos brake shoes, just a bit. I was pleased to see that the inside of the brake drum was still shiny and clean.

The petcock, which was to be replaced with an OEM part, was almost rebuildable, apart from a slotted screw in the retainer face plate instead of a normal cross head screw. The owner had attempted to clean the inside of the fuel tank. We’ll see how well that works out once it is up and running again.

The tubes and rim bands came in ahead of the tires, which were coming from two different locations. Fortunately, the little tires on small bore bikes are generally easy to change with hand tools. The rear tire came in first, so as I extracted the rear wheel assembly, I noticed that the tire was a “Swallow” brand Korean unit in 3.25x18 vs the stock 3.00x18 size. As the wheel was inspected, there were big gouges in the inside of the left chain adjuster, consistent with a thrown drive chain at some point. The bike only had 3800 miles showing and the front tire was definitely the original Yokohama rib showing big cracks in the sidewalls.

The rear wheel sprocket was removed for surface cleaning and the new tire spooned onto the rim. A new drive chain was installed and the whole back end was tidied up as much as possible.

While awaiting the front tire’s arrival, I removed the wheel to clean up the brake cams so the brake action would be restored with a new cable. This left me in a dilemma as the OEM front brake cable has a built-in front brake light switch and these cables are difficult to find and quite expensive. A couple did turn up on eBay, one at $49 and another at $29, but $44 delivered.

The fork seals arrived and with the front wheel in a temporary installed state, I removed it and went about taking the fork legs off. The left side came out easily, but there were ominous signs of rust down inside the chrome sleeve that sits atop the fork slider. Normally these are tapped off with a screw driver around the bottom edge of the sleeve, but this one would have none of that attempt. After spending a half hour trying to tease it off the fork leg, it was apparent that the sleeve was rusted into the fork housing and needed to be replaced. Back to eBay for a set of good-looking forks from a seller in the mid-West for $107 delivered.

The replacement forks arrived, looking very clean, especially at the chrome sleeve junctions. Getting them off without damage will allow for a fork seal replacement and then refilling and installation. Also, the replacement handlebars had a few rust spots, but were miles nicer than what was on the bike as it arrived. All the handlebar switches will be swapped out and then the fresh bars installed with a new set of cables. I was able to track down another of the rare front brake cables with the brake light switch installed for $44, so we’ll keep that function going for these new riders.

I removed all of the headlight wiring connections in order to facilitate the replacement of the bent up handlebars. In the meantime, I laid the bike over on the left side and removed the clutch cover. All the screws had never been disturbed since assembly in 1969, so the use of a 3lb sledge hammer was employed to coax the screws loose. Amazingly, the clutch cover popped off with the gasket completely intact, a rarity in my experience. The clutch plates were a little sticky but didn’t show signs of the kind of “stuck-clutch” feel of the clutch lever when it arrived. A new clutch cable will be installed with the handlebar swap and hopefully the function will return to normal. Happily the inside of the engine looked very clean, owing to its low miles condition.

The new tire arrived along with the cable and handlebars, so a few more hours of work lay ahead.

Winding it down…. 2 weeks later. 

So, the handlebar swap took a good bit of time. I had to saw the bent part off in order to retrieve the switch harnesses. The outer sleeves were all crispy and unwilling to move through the inside of the bars easily. Once the switches were installed, then the bars went onto the bike and all the wiring connectors repaired and connected. The cables had to be installed and routed, then adjusted correctly. The last thing was to drain the very dark oil and check the valve clearances and ignition timing. 

Of course, spark advancer was rusted to the end of the camshaft and it took flooding the advancer with penetrating oil and my heat gun to get it loosened up for cleaning and adjustment. The points had worn down causing the ignition timing to be quite retarded. The drain plugs on these engines uses a 19mm socket for removal. I had to use a 2ft long extension bar to finally break it loose. Ugly oil splashed out into the drain pan. Like every other screw on this bike, it took an impact driver to loosen each and every one of them. Once the dyno cover was removed, the timing could be set and it was looking like it was about to come alive once again, since 1997!

With the carbs done and installed and new oil and timing checks, it was time to hit the starter button!

Thankfully, it burbled to life quickly and sounded pretty good, apart from the extra exhaust noise coming from the muffler holes. I cleaned up the mirrors and installed them for the first test ride since the last century. Happily, it was feeling like I remembered mine back in 1969, in Puerto Rico! I rode it for about 5 minutes, including a good pull up my test hill and it ran perfectly. It’s still on the ugly side due to all the rust on the chrome and alloy bits, but it seems safe to ride and enjoy once again.

Here, in the end of March, I am juggling repairs on the 1961 CB77, a 1964 CL72 and this first of two CB175s. So, depending upon the parts available, the work load was distributed between the three bikes.

The CL72 finished up first, so will be first out of the shop, followed by the Super Hawk. Once this CB175 is up and running, its stablemate twin will swap out for this current project, no doubt with similar ills. So, no doubt the next CB175K3 will get its own story. Then the fraternal twins will be reunited, both in running condition and ready for the road.

Bill Silver

aka MrHonda

www.vintagehonda.com