There’s always a reason… find it! CL175 2.0 to completion.

Welcome to MrHonda’s mystery hour, where we delve into the unexplained behaviors of vintage Honda motorcycles, after normal repairs have been completed. In this edition, the subject in question is a 1969 Honda CL175K3, which had an engine overhaul and carburetor cleaning. The engine starts up easily but then loads up the spark plugs quickly with excess fuel.

Spark plug fouling at idle is generally attributed to either the wrong-sized pilot jets, high float levels, blocked air bleed passages at the carburetor inlet ports, incorrect ignition timing, high resistance spark plug caps, defective spark plugs (fake reproductions), low spark voltage due to failing coils, weak condenser, incorrect cam timing or aftermarket parts which are not made to OEM specifications.

Background information: The engine was brought to me in pieces for a rebuild, including the replacement of the kickstarter shaft. The cylinders were still on STD bore sizes, so the bores were honed and new rings were installed. The original valves were re-seated and all new seals and gaskets installed. It was pretty much a standard engine rebuild.

Once installed, the engine was started up, sounding rough as if it was running very rich at idle and just off-idle. It fuel-fouled the spark plugs in just a matter of minutes. The carburetors had been disassembled and cleaned, noting that one of the slide needles were marked D2, which indicates that they are from Keyster carb kit. The idle jets were also from the kit and marked #38, which is correct for this engine series. The main jets were marked #92, which is stock, but I have had issues with the accuracy of the kit parts in many cases. The bike is a Scrambler, with left-side high pipes, which have to be removed or at least loosened up so that the left-side cover, air filter and carburetor can be removed for service. The carburetors were inspected several times after each start-up with no favorable response to any adjustments done to the needle height or float levels. There was an odd situation where the left side carburetor fuel levels were greater than the right side, despite careful float adjustments. The petcock was checked as it was dripping, even in the OFF position.

The petcock had been installed without a sealing washer for the attachment screw that holds the petcock to the bottom of the tank. Additionally, the back side of the fuel lever was uneven allowing fuel to pass the barriers of the 4-hole petcock gasket. Once the fuel lever was flattened out and a sealing washer installed, the petcock functioned normally. Both fuel lines were matched in length to alleviate any issues with fuel flow to each carburetor.

Having removed, cleaned and inspected the OEM carburetors three or four times, I had to start looking at other associated problems that might have been overlooked or assembled in error. Starting with the basics, the compression readings were about 140 psi, which is a bit lower than Honda’s spec for a normal engine. Low compression readings, when both sides are the same, can be indications of incorrect cam timing. This engine had new rings, which were not seated yet, so some leakage was to be expected. A leak-down test showed nothing abnormal, apart from some air leaking into the crankcase past the new rings.

All indications were that the cam timing was correct, although Honda’s tune up book showed the intake valve opening at 10 degrees before top dead center, and actual valve opening appeared to be starting at about 20 degrees. This might look like the cam timing was incorrectly set, however most cam timing readings are taken at .040” so with that in mind the cam timing was correct. I actually removed the top cylinder head cover to verify that the marks were correct, which they were. So, take that off the list of possibilities.

I observed that the aftermarket replacement ignition points were contacting at the very edge of the contact faces, rather than in a more central location. A bit of bending of the stationary contact brought the contact back towards the middle. The gap was rechecked and timing adjusted to suit. The spark advance was checked for proper function in advance and full retard positions. The ignition coil was an aftermarket replacement with the original spark plug caps installed. The caps were measuring about 10k ohms, instead of the preferred 5k ohms, so were replaced. So far, no “smoking gun” was found to cause the rich running of what appeared to be stock OEM or replacement parts.

A set of aftermarket, Chinese-made carburetors had been brought down originally, so in desperation, they were installed. These replacement parts had their own issues. The “set” was actually two right-side carburetor bodies, so that both had the carb adjustment screws on the right side and fuel feed fittings on the left side. Both carbs had the same slides with the same cutaways, as that is what a right-side carburetor would be equipped with.

The carburetors were fitted to the stock intake manifolds which had been flattened off with my little belt sander to ensure flat contact surfaces. Once fitted, the bike was started up and immediately ran cleaner and idled down comfortably without the rich running that was occurring with the “stock” carburetors. At this point I was truly baffled about why the stock carbs failed to function properly, and a set of Chinese carburetors, which had no markings on any of the jets, were working normally.

However, the Chinese carburetors had a different issue. The next day, the bike was hard starting and only ran on almost full choke. As it warmed up, I slowly lowered the choke lever until it would start to stall out again, which indicated that the needles needed to be raised up a bit. The right side needle was a 5 notch type with the clip all the way at the top.. so super lean. I moved the clip to the middle groove. The left side needle came out and was a completely different type with only 3 notches! I went for the full rich option and restarted the engine again. Like magic, the bike took throttle, off idle, and was smooth and responsive in a 5-minute test ride.

I reported this limited success to the owner of the bike project, but could not give a cause for what had happened… until I went to put the old carbs into a box for storage.

Looking carefully at the carb needles, I finally realized that they were of different material. One was a brass D2 Keyster needle, but the other silver-colored needle was not marked at all. Comparing the two, the profiles of the needle tapers were different, as measured with a caliper. Ah, ha! Maybe I was on to something important, after all. Then, I flipped over both of the carb slides, which appeared to be the same, as far as the material and coating was concerned, but then was shocked to see that one slide was an OEM Honda part and the other one was not marked at all! Sitting them side-by-side, I could see that the slide cutaways were a bit different and then looking even more closely, the whole slide bottom, where the needles are located were at a different height! The aftermarket slide was a completely different part, as far as dimensions go for the needle and the cutaway. Eureka, I found it!

I was able to track down a set of OEM needles from an eBay seller, then went to cmsnl.com for the other needle, plus a new OEM slide, plus a pair of OEM idle jets. I now have confidence that with the correct OEM parts installed, the stock OEM carburetors should work normally, as designed. It’s been an arduous task with many hours of removing, inspecting, cleaning and installing the stock carbs over and over again, expecting a better result. I think that has been described as “insanity,” isn’t it?

I thought that this was the end of the story, however the bike had other ideas. When the fueling issue seemed to be solved, a long downhill run, a part of my testing process ended when the bike slowed down for a corner and then went completely DEAD! It had blown a 20 amp fuse. I had no other fuses with the bike and I was stuck a mile away on an uphill return. I called a couple of neighbors and neighbor Paul picked up the phone during his grocery shopping and said he would come and pick me up shortly.

I pushed the bike up an angled cement corner, made for wheelchair access, and left it under the shade of a palm tree. Paul came by, picked me up and dropped me at home. I loaded up the Tacoma and headed back down the hill to where the bike awaited my return. Loading a 280 lb. bike, even with my long ramp into the Tacoma can be challenging, but when I arrived at the bike a somewhat scruffy man was sitting next to it, accompanied by his dog. We spoke about the bike and what had happened. I could tell that he was looking for signs that this was my bike and I was the rightful recipient of it. He happily helped me load the bike into the bed of the Tacoma and walked back to his waiting Honda Accord, with the dog in tow. How amazing that someone came out of nowhere to help out just when I needed it the most!

I unloaded the bike and set to work finding the cause of the short. The bike only has one fuse, so when it is blown you are completely inoperable. I have a resetable relay connected to a set of wires with clips on the end. You can put them on the ends of the fuse holder and it will click on and off, when a short is present. Of course, it seemed perfectly fine all of a sudden. I did track down some worn wire for the rear brake light, which was repaired. Also, the fuse, in the fuse holder, should have been a short 15A fuse, but was a longer 20A fuse. The length of the fuse, caused the ends of the wires that attach to the fuse holder to extend out beyond the plastic fuse holder. That made them vulnerable to contacting a grounded frame area and create a dead short. I put a shorter fuse in the holder and pushed the wire ends into the plastic holder out of harm’s way. Nothing else was evident, so I turned my attention back to the carburetors.

On the next short run, partially down the hill, the bike ran well for about a minute, then went off on one cylinder. I slipped the clutch and revved the engine sky-high to try to get it back home again, just a quarter mile away. After it sat for a moment, it suddenly caught on again and I nursed it back home again. The problem was that the right side carburetor was running out of fuel, while the left side was doing fine. I rechecked the float level with the carb still installed and looked for any signs that perhaps the float was somehow contacting something inside and shutting off the fuel flow. I did another around-the-block test and it started to run on one cylinder again. No matter what I did, it wouldn’t keep fuel in the right carb bowl.

I had already bought another aftermarket petcock, in case there were problems related to the one that came with the bike. I drained the tank and removed the petcock. On more careful inspection I noticed that the two holes that feed the fuel lines to the carburetors were not on the same level. Wow! Could this be a factor in the fuel feed issue? The new petcock had a little screen on the reserve port whereas the original did not. Grasping at straws, I installed the petcock and hooked everything back up. Again, the fuel wouldn’t flow into the carb unless the bowl was dropped down and the float allowed to open the float valve.  The replacement petcock had its own problems. The space where the attachment screw is narrowed more than stock so the proper screw gasket (not included with the petcock) doesn't fit! I had to slowly grind down the OD of the gasket so it would fit snugly down and seal the screw head.

A friend suggested that I try another float bowl. The OEM carb bowls fit right up to the Chinese copies, but the result was the same. I removed the air filter and the carb from the studs to have another look at the bowl venting system and rechecked the float level with the carb held on the side, with just the weight of the plastic floats touching the needle. The measurement was different in that angle, so was re-adjusted again to 21mm.

Comparing the float bowls, I noticed that the brass overflow tube on the aftermarket carburetor had a really tiny hole. The carb had flooded over previously, so I knew that the passage was opened. But when I compared the OEM bowl to the A/M version, the original brass tube had about a 1.5mm hole vs about half of that on the copy. I opened the tip of the tube up with my 1.5mm drill bit and put it all back together once again. I turned on the petcock, waited a minute and then shut it off and removed the float bowl. It was FULL! 

I re-installed the air filter and side cover and went for a short ride just to test the performance. It was greatly improved and only hinted at a big of richness just off-idle. I removed the mismatched aftermarket needles… yes they were not a match on the same set of carbs, too! I compared all needles from both carbs and discovered that the D3 needle was match for the other brass needle and the two silver needles were also about the same. I dropped the needles down to the #2 groove and reinstalled them again. Suddenly, the bike felt and sounded like a almost normal CL175 Honda twin again. I brought my fuse tester with me, just in case, but made the full downhill test run back to the place where the fuse had blown before and then turned back around for the return leg. It was running well; as well as it could on aftermarket carbs and a mix of non-OEM carb bits.

Bill M. was on his way down to pick up the CL175 and leave me an XR75, plus the chassis for the SL100 engine that I had finished rebuilding. Obviously, I was very pleased to have finally conquered the worst of the bike’s problems and felt it was safe to drive regularly. I would feel even better once the OEM carb parts arrived from Holland. At some point the original carbs can be returned to the engine, for which they were intended.

I lost track of the actual hours of work devoted to analyzing and developing some strategies for a successful outcome. In the end there is a sense satisfaction that perhaps I learned something new, when facing similar challenges in the future.

Well, it certainly had me going round and round, unfortunately overlooking what was obvious in hindsight. It’s difficult enough to repair these old bikes given the lack of original parts, here in the 21^st Century. While the aftermarket vendors try to supply the needs of owners, unfortunately, the lack of quality control and design detail can cause a world of frustration, in cases such as this.

In situations, such as this, when nothing makes sense, even though you think that everything has been done correctly, you have to backtrack and dig deep into the minutiae of the smallest details. A small discrepancy can derail your best efforts to troubleshoot and diagnose the problem. In the end, you will find success.

Bill Silver

aka MrHonda

www.vintagehonda.com

08/2024

CL175K3 Blue tape special

A few months ago, my friend Bill M. contacted me about “rebuilding” a CL175K3 engine for a project that he was doing for one of his friends. The plan was for him to bring me the engine to rebuild and he would be restoring the chasssis then bringing that down here for the engine installation and then put all the bits and pieces back together again. The bike was purchased as a partially started project from a previous owner and the whole bike was disassembled.

The engine arrived with the lower end in a screwed-together wooden box, while the top end and carburetors were in separate bins. After about 15 minutes of undoing all of the wood screws, the bottom was revealed to have a damaged kickstarter shaft. A new one was provided, so this was obviously going to be a full teardown and repair. The engine was otherwise in decent condition internally, but required cylinder honing, valve seat repairs, vapor blasting and installation of the fresh parts. It was still on STD bore and the pistons were reused along with new rings.

Whoever started the project, was apparently new to the hobby, so virtually each and every single part was labeled with blue masking tape, including all of the wire connectors. So, part of the process was to peel off all of the blue tape from the components and clean the parts of  the remaining adhesive.

The engine rebuild was mostly uneventful, apart from having to run around town, hauling the parts back and forth to my friend with the vapor blasting machine. A set of aftermarket carbs were brought along with the engine parts, but the originals seemed to be worthy of a good cleaning and kit installation.

Once the engine was completed, it sat for a couple of months while I was doing several other projects and waiting for Bill M. to finish the chassis and find time to marry the two project halves together. Finally, in Aug, fully four months later, the the chassis was delivered on an early morning trip from OC and work began. The engine was shoehorned into the frame and all of the engine bolts fed into their respective places. Bill had brought down a copy of the parts manual, so we could refresh ourselves about what went where and what might be missing. Slowly, on a very hot day, the bike began to take shape, rising like a Phoenix from the pile of parts emerging from their blue-taped packages.

The CL175K3 model is the only one that had a high-mounted front fender, which was composed of several various adapters to fit the bottom of the fork stem. According to some parts lists, the K3 was sold in 1969-70. The wiring harness was fed back into the frame recesses at the back of the chassis and the ignition switch mounted up on the forward bracket, beneath the gas tank on the left side. A charged lead-acid battery was pulled from its box and dropped into the battery box. These batteries have a vent tube that needs to be routed carefully, to prevent acid damage to the chassis during operation. I situated the battery so the vent was towards the rear of the battery box.

At first only the neutral light came on when the ignition switch was switched to the ON position. The bike had been supplied with a little aftermarket cube bridge rectifier in place of the OEM selenium unit which mounts on the inside of the frame behind the carburetors. When I touched the battery ground lead to the battery there was a strong arc, indicating some kind of short circuit. The only thing that is active when the key is OFF is the rectifier, so I assumed that it had a defect and we ordered a $100 OEM unit from an eBay seller.

In the meantime I was puzzling over the other electrical system issues, starting with the tail light function. Whenever a bike chassis is powdercoated or even painted, all of the ground paths need to be established again, as the powdercoat becomes an insulator to electrical circuit pathways. I had cleaned off the usual places for proper grounding but when I checked the power to the tail light, it showed power to and through the bulb, but my test light lit up only when it was grounded back to the battery. Studying a copy of the online wiring diagram didn’t show any separate ground path to the harness wires, except though the various components, but they were still mostly isolated from a good ground path. I finally eyed a single green female ground connector by the battery with no place to go. I made up a jumper wire and connected it to the female connector and grounded the other end where the turnsignal flasher mount bolts to the frame. Success! All the lights came on and power seemed to be restored to all of the lighting and other functions.

A few days later, the spendy orange rectifier arrived and was installed after removing the left side carburetor again. The mounting stud was well grounded and I was looking forward to completing the electrical system. But, as soon as I touched the two harness connectors together, there was a big flash and wires started getting melted! I quickly pulled the two connectors apart and reviewed the wire colors for each side. The harness side connector had the red hot wire across from the green ground wire, but these colors were swapped on the rectifier side. Obviously this was a dead short to ground for the battery feed line. I pushed the wire connectors out of the harness side to match the rectifier colors and plugged them back together again, gently. There was still some arcing going on, but less than before.

Finally, I thought to check the battery connections and finally noticed that the battery was installed BACKWARDS! This was the cause of all of the electrical arcing from the rectifiers, both the aftermarket one and the OEM version. MrHonda had a senior moment and hadn’t paid attention to the battery polarity. The battery was installed with the markings turned away from me and I was using the position of the battery vent tube as the indicator of the orientation of the battery when mounted in the frame. It all became clear in an instant and now the damaged rectifier needed to be removed and replaced again. In looking at the rectifier, only the green ground wire that comes from the connector to the side of the rectifier mount was fried, so the rectifier through bolt was carefully removed, and a new wire with a ring terminal was installed. With everything re-attached, there was no arcing when the battery was re-connected and all of the rest of the electrical functions were operating normally.

In order for the Scrambler exhaust system to be installed, the left side air filter must be attached to the carb and then the left side cover snapped into place. Then, the wiggly Scrambler exhaust pipes can be hooked back into the exhaust ports and attached at the rear mount. That done, the bike was rolled off the work table and down to the driveway where the fuel tank was waiting to be installed.

The petcock appeared to be an aftermarket piece, already connected to fresh hoses and inline filters. The petcock mounting bolt was missing the sealing washer, so I had to dig up one from my pile of leftover carburetor parts. Then the screw wouldn’t go into the tank without chasing the threads with a 6mmtap. Once everything was put together, some fuel was poured into the tank and the moment of excitement arrives. The original kickstarter which had flattened out splines was replaced with an aftermarket piece which was an inch shorter than the OEM unit. This made kickstarting a bit of a chore as it was near the rear footpeg. I had already checked the ignition timing, so it should have fired up quickly. After a dozen kicks it coughed to life reluctantly, then stalled out. I looked down to see gasoline dripping down from the left side of the engine and oil dripping down on the right side of the engine. Now what!!!!!?!?!??!

The left side carburetor was dripping from the overflow tube and even with the petcock turned to the OFF position, there was still a persistent leak. The right side leak was from the oil filter cover, which had been sealed up with new o-rings, but continued to leak after several inspections and measuring the o-rings for the proper sizes. I happened to have a spare outer o-ring so stacked two on that side and the oil leak ceased. I tried to access the left side carburetor float bowl to see if something was obviously evident, perhaps with a failing float from a pinhole. It always seems that if you are working on a Scrambler of any size the left side carburetor is the one that will have an issue.

The exhaust port gaskets were supplied from an ancient gasket kit and consisted of some asbestos wrapped with copper wire. These compress down to nothing when installed, and the result was exhaust leaks at the flanges. The pipe packing that seals the two exhaust pipes together at the rear junction was mostly gone, so there as a leak back there, as well. So, the tank came back off so the petcock could be rechecked for the dripping issue and the exhaust removed again for new seals. With the exhaust removed the carburetors could be reinspected again. The left side drips had stopped, but when the engine was running briefly, it sounded like it was running rich on the right side, which was confirmed by a black plug when removed for a compression check,

New parts were ordered and the bike’s carburetors removed and checked again. There were aftermarket kit parts installed and they are often not to OEM specifications.

In the meantime, more electrical work was required to reconnect all of the wires inside the headlight shell. The rubberized instrument lights that pushed up inside holes in the back of the speedometer and tachometer were mostly all toast. A previous person had wrapped a lot of black electrical tape around the bulb sockets in an attempt to keep them situated in the lighting holes, but obviously, this was a failed attempt. I happened to have a string of instrument light wiring from a different model, but all of the socket rubbers were in great shape. I snipped here and there, finally getting them all spliced in for functioning instrument lighting. I had to special order the 12v 3w light bulbs to fill all the empty holes.

When I went to fit the headlight assembly back on, the left-right adjustment screw and bracket were broken away from the back of the reflector. When the rim was test-fitted to the headlight shell, it became obvious that the shell, which is metal, was out of round and painted that way along with the other metal parts (plastic side covers) on the bike.

I had some various woodworking clamps hanging in the shop and one was big enough to reach around the perimeter of the shell and with some strong twists of the clamp, brought the shell back to a circle once again, without damaging the painted surface. The left side headlight bracket had a bend in it, which needed straightening. The bike had surely been crashed at some point and the damage was left unattended by the painter and previous owner. Finally, all the lights started to function, but the headlight assembly isn’t centered with the midline of the front wheel, so more work needs to be done there.

The bike was run on and off my work table, to the driveway near the garage door opening for follow-up work on the fuel system. Repeated removal, inspection, cleaning, adjusting and re-installing of the carburetors failed to remedy the fuel fouling of the spark plugs. A more detailed examination of the associated components in the ignition and fuel systems didn’t give a solid clue as to the cause of the carburetor problem. It was finally resolved when a comparison of the needles, slides and idle jets revealed that the aftermarket parts were not a perfect match to the OEM parts.

See the next story on CL175 troubleshooting for how the process was performed and how it was finally resolved after hours of trial and error, including the replacement of the stock carbs with some Chinese copies. 2024 has brought in very difficult project bikes to sort out and rebuild to specs. It ain’t easy being MrHonda sometimes.

Bill Silver

www.vintagehonda.com

8/2024

Another day, another Scrambler….

Well, they just won’t stop coming. Latest bike is an early 1964 CL72, painted orange, supposedly from the selling dealer with some 1963 features, like a sand-cast front hub and even the oil pump. It was in overall nice condition, but the owner complained about the transmission shifting erratically and the engine had been freed up after weeks of soaking and heat until it finally freed up. He was able to get it started and running, but the engine rpms were uneven and the head gasket was leaking. He had also swapped out the clutch fiber plates with Barnett performance parts, but kept the original springs.

After drop-off and initial evaluation, I dove into removing the 100lb lump and began tearing it down for inspection and a full overhaul. I had to drill the heads off of three of four cylinder head side cover screws to start with. Once the top cylinder head cover was removed, the camshaft lobes looked a bit rusty around the edges. Apparently, the bike was either mostly original or rebuilt and then left sitting for something like 20 years. The camchain tensioner was removed at the back and the roller was seized up solid. Somehow the long-term storage had created some moisture inside the tensioner roller pin and bearing, locking it up.

Pulling the cylinder head off, yielded some surprises. Usually, when “stuck” engines are freed up, the result is the rings have been stuck in the piston ring lands, causing a loss of compression. The owner initially tried to do a compression check with a push-in gauge and found 90 on the left and 140 on the right side. Before he left, we used my screw-in compression gauge and got 175-180 readings on both sides! The tops of the pistons had a little layer of black carbon from oil burning and perhaps carb metering problems. When the cylinders were raised, the rings were all free in the pistons and the pistons were all STD size. The edges of the rings were really sharp, having scrubbed all the corrosion off the cylinder walls that had kept the pistons stuck in the bores. Removing the top compression ring and putting it in the bottom of the cylinder bore gave me a .032” gap, which should have been about .006-008” normally.

I used a ball-hone to scrub the cylinder walls, to determine how much corrosion damage had occurred but the bores looked surprisingly clean. There was a bit of a corrosion ridge/ring just where the top ring lands, but I was seriously considering just buying new rings and re-using the pistons again with the cleaned up bores. Finding machine shops here in San Diego, has become increasingly difficult as the guys who have been in the business for many years are aging out and suffering from various ailments.

Calling my friend Tim McDowell in MD, to order some gaskets, seals and a screw kit, lead the conversation to mention that he had a whole set of cylinders, bored to. .50 oversize with pistons, rings, clips all ready to go! We made a deal on the whole package and it was shipped out quickly.

In the meantime, the bottom end was dismantled including the revised clutch parts. Nothing much was amiss but the oil filter was somewhat tight on the shaft. Once the cases were cleaned off of all the clutch and shifter hardware, they were separated for the inspection of the transmission gear dog overlap. As suspected, the 2^nd gear dogs were a bit rounded off where they were clashing against the adjacent gears and the overlap was minimal. This is not unexpected given the early production of the engine, as most are similarly found to be lacking in overlap.

As a bonus, the owner brought down two big plastic bins full of “extra” parts, including a couple of transmissions. I sifted through the transmission sets and found a nice 2^nd gear, plus a NOS shift drum! The transmission gear cotters were removed so I could do the X swap in the gear ratios and the cotters that came out were offset ones! So, after some mix-matching of gears and cotters, the transmission should be in the best possible condition. I did replace the low gear bushing with one of the new reproduction pieces and the kickstarter pawl which was wobbling in the end of the shaft. The end bushing had some usual wear from the pawl rubbing up against it, so I decided to try to find a thin thrust washer to make a better surface for the kickstarter pawl to push up against. I found what seems to be a possible candidate with a Kawasaki washer that was ordered online.

The engine cases, cylinder head and associated covers were taken to a local engine rebuild shop for de-greasing. There was a lot of black goo inside the engine surfaces, partly from the camchain rubbing up against the seized roller when the engine was running. There was the usual gunk that covers the bottom of the cases, due to the use of original non-detergent oils, which were recommended by Honda in the early days.

The head was stripped of the cams, rockers and camsprocket before cleaning. The camsprocket weight springs were really loose so the ignition timing was all over the place when it was first started back up. The sprocket was sent to Tim Miller, in TX who specializes in building racing 250-305 engines and has come up with an effective rebuild for the sprockets, which lessens the total advance. This allows for the idle timing to be at 10 degrees BTDC instead of the usual 5 degrees, which Honda used. The added 5 degrees makes for a happier engine idle overall. New valves were ordered from DavidSilverSpares and the head was taken back to the machine shop for seat grinding to ensure full compression.

Little roadblocks…

Well, the nice NOS cylinders from Tim McDowell, which came with .50 MC pistons, turned out to still be on STD bore sizes, so with a fresh set of STD rings, I can reuse the OEM pistons and solve that problem. HOWEVER.. the NOS cylinders was a late-model die-cast unit, which uses the narrow 32mm tensioner that I didn’t have in stock, I had ordered the Capellini tensioner sprocket kit for use on the wide tensioner that came off of the stock cylinders. So, now I have to scrounge around for a usable narrow tensioner body and remove the old roller or Option 2 which is a NOS tensioner on eBay, but the tensioner doesn’t come with the spring and bar to push the roller out against the camchain. These parts are specific to the -020 tensioner assembly. Just when you think you have your ducks in a row……

Well, I did both.. bought the new tensioner and then discovered that I had a used one in the engine parts box after all. Problem solved.. or not?

The rebuilt cam sprocket came in and was carefully installed on the endless camchain. It’s a tricky proposition and required clamping the top end down with some sockets and nuts so I could join the two camshafts into the master spline of the sprocket. Once that was accomplished, it was time to install the camchain tensioner… and it wouldn’t fit into the back of the cylinders. Perhaps the Capellini parts are slightly wider than the originals, but it appeared that there was some casting flashing in and around the tensioner hole that was jamming the tensioner arm roller hardware. I tucked some shop towels into the opening and then carefully ground out the insides of the cylinder opening. It helped but still needed a bit of a push to clear the opening and finally fully install.

The cams and top-end bearings were all lubed up and the top cylinder head cover was installed. The top nuts were torqued down and only the oil pump installation is left after the engine is flipped over to expose the bottom end.

It takes over an hour to either remove or reinstall the engine assembly, given all the little bits to round back up and re-attach. I used a remote fuel bottle to connect to the carbs and with a half-dozen kicks the engine fired up and sounded pretty healthy. I had set the ignition timing statically just to get it running, but the project stalled until the requested Pro-Trigger electronic ignition system arrived from Florida. In the meantime, I noticed that when I rolled the bike around the massive 4.00x19 rear tire was making flat tire sounds. The tire is so large and so old that there are no date codes marked on the sidewalls. Checking air pressure, none was found. I aired-up the tire to 30 psi and shortly thereafter it went back to zero. I called my local shop to check on inner tube availability and thankfully they had one in stock. I removed the wheel assembly and hauled it down the eight miles to National City Motorcycles, where the owner, Rob, put it on his tire machine and replaced the tube and rim band.

After a few days, the ignition system arrived and was installed. It’s a bit fiddly because the trigger wheel with the magnets is just a round section of aluminum with no indexing to setup the correct timing. It’s a bit of trial and error, but eventually, the timing came in correctly and the bike was fired up once again. Winding down the final adjustments, the tank and seat were re-installed and the first test ride done, just around the block. Because the crossover tube fittings had been blocked off by the owner to reduce the fuel spilling when the tank was removed, the fuel supply to the petcock is somewhat limited to the right side of the tank. There seemed to be sufficient fuel in the tank, so a longer test ride was undertaken. The usual route is about a mile, down a long hill to a turnaround at the bottom.

I could feel it dropping a cylinder as I reached the bottom and finally it quit altogether. Rechecking the fuel supply on the petcock side and turning the petcock lever back and forth between On and Reserve, got it fired up again, but it only went about a quarter mile back up the hill before it quit again. I pulled the fuel lines off to the carburetor and nothing was coming out in reserve, but fuel did flow in the On position. The bike fired up again and I made it back home, avoiding the drama of calling a neighbor to come and fetch me, then returning with my truck and having to load up the bike for the ½ mile trek back to the house.

The bike was fitted with the yellow MotoBatt battery, which are generally very reliable. I noticed some corrosion build up on the terminals, which I hadn’t seen before on any of these batteries. Finally, I decided to check the voltage with a meter and the news was grim. 10V with the key off and 9v and dropping with the key On and the headlights On. When the bike was fired up again, the voltage continued it’s decline… the charging system was not working. I gingerly fished out the rectifier which was one of the later solid-state units, instead of the orange selenium units normally found on early bikes, but the test results were zero. It was a dead soldier.

I fished around and found one of the little cube full wave bridge rectifiers, that Radio Shack used to sell and with some connectors and extra wire, the unit was installed in place of the old rectifier. I had put the battery on the charger for an hour or so, which indicated 12+ volts at rest, so reinstalled it and started the bike up again. The voltmeter jumped up towards 13v, even at low speeds, so the electronic ignition was getting a full dose of juice as were the ignition coils. One more problem solved, but one more to go. Even after the battery was charged, the battery voltage dropped from 12 to 10 with the key On, so a new replacement was ordered.

I removed the gas tank and laid it on the left side so the fuel went to one side which allowed for removal of the petcock inspection. I was surprised to find that there was no brass tube fitted to allow for a normal ON fuel feed, before requiring the Reserve to finish draining the tank. Then, as I continued to inspect the petcock body, I realized that there was no reserve port function in the petcock body. If I had installed a brass tube into the petcock body, there would be fuel leftover as the level dropped and no way to finish using up the remaining fuel. This explained why there was no fuel flow in Reserve position as there is no way for fuel to exit the petcock. I removed the petcock body and probed the little fuel feed ports, finding some leftover debris and scale in the On port. So, with the understanding of what had been happening with the petcock and low voltage, I was getting more confident that the bike was okay, overall. However, the shifting issues were particularly troubling during the test rides. The petcock continues to perplex me, as I have never seen that before on a stock Honda petcock.

I had replaced the low gear bushing and re-shuffled the clutch pack to allow for clutch plate retention which was not possible before with the replacement clutch pack installed by the owner. I installed some of the offset cotters to help engage the gears, but had used some of the rare deep offset cotters, which were giving almost 90% gear dog engagement. In reflection, you can do too much of a good thing and the deep engagement may have been causing the gears to remain engaged rather than releasing easily when the next gear selection was chosen. Mulling it over in my head, the only sensible solution was to remove the engine once again, split the cases and re-do the transmission cotters. So, out it came again…

In the tear-down, I revisited the clutch plate stack and decided to replace the center hub with the later 5-plate version, which uses a thick Plate A and just one set of plates after that, using the retainer wires. This allowed the clutch plate set to more easily spin free at idle. Clutch drag at idle is a big cause of shifting problems, especially when finding neutral at a stop. These transmissions were designed in the late 1950s, so they can get caught up between gears, at times, if the shift selection isn’t done with some authority.

I replaced the .040” offset cotters with a set of the .020” versions, which reduced the gear dog overlap back towards 50-60%. There was some end play in the countershaft that causes the kickstarter pawl to get a bit cocked as the shaft moves in and out. I had ordered a 1mm thick thrust washer online that was a Kawasaki part and was able to insert it into the shaft next to the end bushing, which took up all of the end play without jamming the shaft up between the bearings. I sealed up the crankcases once again and reassembled the primary side with the updated clutch parts.

It was another hour of installation time ( 5 hours overall to R&R the engine and make repairs), but I was feeling more confident that the major problems were being addressed. Unfortunately, the right side carburetor started to drip from the overflow tube. The float was slowly sinking due to a pin hole so that was replaced. The drip continued once again and the float valve needle was replaced, finally stopping that leak issue. One final check of the spark plug caps turned up the left side with 17k ohms instead of the preferred 5k ohms. So, with that replaced, the bike started running better and better. 

As you can imagine, lots and lots of labor time is involved in doing the basic overhaul work, then sorting out all the associated problems discovered in the repair process in these 60-year-old machines. People who work on these bikes begin to appreciate how many problems arise and the amount of time and effort it takes to make them return to their former glory.

Bill Silver

aka MrHonda

8/2024