O-ring confusion for 250-305 Honda twins

Super Hawk and Scrambler twin carburetor models

While the port sizes on the twin-carb heads are basically the same for either a 250cc or 305cc engine, the Bakelite insulators have different markings and ID holes. The 250cc bikes received 22mm carburetors and the 305s are fueled by 26mm mixers. The 29mm o-rings with part number 16173-260-004 should be used on both the carburetor flanges and the matching insulators for the 305cc carb installations. 29.0 X 2.4 16075-GHB-B70 and/or 91304-KPH-700 are other part numbers with similarly-sized o-rings for 305 twin carb applications.

The 250cc Super Hawks and Scramblers can use the 91302-PF0-003 O-RING (26.9X2.4) parts on both the carburetor flanges and the insulators. Unfortunately, many Honda parts listings are showing the 91302-PF0-003 O-RING (26.9X2.4) as appropriate for the 305s, when they are actually sized only for the 250cc 22mm carburetors used on CB/CL72 models. Many Honda part numbers have been superseded to something newer that “almost fits” with some effort and in a few cases the “interchange” attempt has gone wrong and often unnoticed except for people like me and a few others! Check current online Honda microfiche listings for CB77/CL77 cylinder head and you will probably see the PFO O-rings listed there instead of the 260 code parts. They won’t work!

CB72 listings show O-RING (27X2.4) 16173-253-004 for the carburetor. Cylinder head listings show O-RING (26.9X2.4) 91302-PF0-003 (replaces 91301-253-000), but that 91301-253-000 O-ring is shown as 28.5mm.

Dreams (single carb models)
On the CA77 images for the cylinder head, we see: 

O-RING (26.9X2.4) 91302-PF0-003 (replaces 28.5mm 91301-253-000 ?) 

For the carburetor section the listings show O-RING (24X2.4) 16173-250-004 (replaces 16173-202-004. (FYI a -202- code part is for a CA95 Benly with a 20mm inlet size). The problem being that the Dream carburetor inlet is 22mm size, but the carburetor flanges have a 32mm groove in it, so these do not fit.

O-ring options from Honda for the Dream carburetor flanges are now:

31.7 x 2.4 91307-958-003

32.5 x 2.4 91356-ME4-003 

32.5 x 2.5 91307-MC8-005

When working with “almost the right size” o-rings, you can often get them to seat into the grooves well enough for assembly and effective sealing. Ones on the small size can usually be stretched into place. If they are a bit on the large size, a little squeezing down can be tolerated within the groove space. There are some SAE near equivalents at www.zoro.com and www.grainger.com if all else fails, but measure carefully, as some offerings are listed by OD (outside diameter) and others are ID (inside diameter). 

MrHonda’s “not for profit” CL90 sale completed…

It’s funny how just about anything that you put up for sale (vehicle-wise) puts up a fuss and fails to cooperate when it is given the opportunity to move onto greener pastures. 

After countless hours of building/rebuilding just about the entire derelict CL90 chassis, which was married to a S90 gas tank and half of the engine, the bike failed to start up on the night before it was to be picked up.

This funky bike’s story continues on with the buyer contacting me from a Craigslist posting, showing interest in it, but he lived 500 miles away in San Jose. Just last week, I was able to secure a PNO title only for the bike after repeated inspections. Once the pending title was secured from DMV, the buyer stated that he was coming down to San Diego and would pick up the bike with his rental car; in this case a new Toyota Highlander! After some “negotiations” for an even greater discount of the $995 asking price, (including boxes of spare parts), he did show up early on Veteran’s Day morning ready to test ride it before concluding the sale.

Almost as an after-thought I decided to check ride the bike once more, only to discover the “non-starting” gremlin had returned. The bike had run beautifully after jetting was worked out, with easy starting and a nice steady idle. Suddenly, we are back to square one with no spark to the plug. In the process of troubleshooting the problem, I used a screwdriver to flash across the open points in order to complete the ignition circuit. It worked randomly, acting somewhat like a failed condenser. Prying the points apart with the screwdriver tip I sensed that something was amiss with the ignition points. 

Moving them open with the screwdriver revealed a sense of sticking on the contact arm.

This ignition plate was the original S90 part which was once submerged with water, leaving a high-water mark on the inside of the points cover and across the point plate. The plate was disassembled and soaked in a rust neutralizer solution to help recover the surface condition. The points were left in place during the process and the refreshed point plate reinstalled into the cylinder head opening. For the most part the ignition worked okay, but randomly it would lose spark and there was no clear clue as to what/why this was happening. Once the point plate was removed from the cylinder head, the point arm could be more easily moved on the pivot pin and it was apparent that this was the problem for the point’s motion failure. With the points removed from the plate, the tiny screw hardware for the point wire was removed and the point arm gingerly pulled off the pivot pin. There were signs of corrosion inside the point arm sleeve bushing and certainly greenish corrosion on the pivot pin, as well.

The pivot hole was cleaned with a quick pass of a drill bit, while the pivot was scrubbed up and lubricated. When the two components were reunited, the pivot action of the point arm was greatly improved. The point plate was all reassembled and placed back onto the cylinder head cavity. The point plate had been marked as to where it was located in the head to set the initial timing, but when the engine was kick-started there was no immediate response apart from a very loud backfire BANG! The dyno cover was removed to allow access to the rotor markings and the engine turned over with a 14m wrench. Suddenly the ignition timing was about 40 degrees late and the points were barely opening at all. Apparently the clean-up pass with the drill bit overdid the arm’s original ID and now the points were somewhat loose on the pin and the point gap was nearly zero.

The engine was turned over until the point cam was at the highest location and the points re-gapped to the normal .014” or so. The adjustment slots were at the end of the travel, but it was just enough to get them into specifications again. With the point plate shifted appropriately, the firing marks lined up once more. The engine covers were re-installed and the bike started on the first kick. Well, that problem was solved, but the neutral light hadn’t worked since the bike was put back together again. Opening the headlight found a bulb socket with a tiny blown 6v bulb at the end. These are very uncommon bulbs, not to be found at an auto parts store. Digging back into the S90 spares, the old speedometer had the bulb and socket/wire still attached. Luckily, the bulb was still okay and finally the neutral light turned a nice soft green color again. That was as far as I could go with the bike, so I took the tools back to the shop and awaited my customer’s arrival.

After his test ride and inspection of the paperwork I had on the machine, we tried to wedge the bike into the back of the Toyota SUV. Unfortunately, the back seats did not fold down fully, but did tip forward somewhat. We had drained the gas tank and removed the battery so the bike could lay on the right side away from the crankcase vent passage on the left. The rear tailgate wouldn’t close so the front wheel was removed while the bike was lying in place and that gave enough room to close the rear door safely. Finally, an hour after their arrival, the happy couple drove off into the horizon with the CL90 nestled in the back of their rented Toyota Highlander. Their next stop was Sea World, then off to San Jose on Saturday where the little CL90/S90 hybrid will find a new home with an enthusiastic owner.

In the end, I think I broke even just for the investment in parts and services while the bike was revived. If it had been a customer repair job, the labor charges would have been close to the selling price alone. While being retired doesn’t require that a profit be made on every one of these rolling waifs, I do need to be a lot more selective about what to revive and what to let go as-is with a “Sorry, I can’t do that this time!”

Give’m what they want…

Tuning/repairing old vintage Hondas (and other makes/models) often requires going beyond whatever it says in the factory repair manuals. When bikes are brought back to life after many years, sometimes the process is straightforward and direct; clean the fuel system, replace the battery, adjust the valves, set the ignition timing and off you go! Other times, they defy all the standard settings and you are on your own to discover the blocks to a good running machine.

My recent experience with swapping a rebuild S90 engine into a CL90 chassis lead to many problems, just from a design and structural viewpoint. The “early” S90 has a different set of engine cases, intake manifold system, exhaust port angles differ, different clutch cover, dyno cover and other smaller features which created parts problems and finally required re-rebuilding the engine using the correct matching CL90 engine cases. Even though these 90cc OHC engines were part of a long-running design, substantial changes occurred in the first year or two and that created more problems to be considered.

Once the engine components were swapped back into the stock cases, the carburetor settings were different from one series to the other, calling for careful tuning steps to be followed in order to get the bike running properly again.  At first, the engine was running rich (starts with no choke) and fouling the plug, while wafting a bit of oil smoke out the exhaust pipe. The engine wouldn’t take even half-throttle with no load on it. Backtracking on my adjustments, it was discovered that the point gap was out around .018” instead of the normal .012-.016” settings. This can cause a loss of coil saturation and subsequent misfiring that can mimic carburetor problems, if you aren’t careful and observant. In trouble-shooting and/fine tuning efforts, you have to make ONE change at a time, re-evaluate and then try something else if necessary. In this case, the point gap wasn’t a significant issue, so I moved onto the carburetor settings.

Current “wisdom” is that with today’s fuels, you need to richen up the fuel curve about 10% in order to compensate for diluted gasoline energy potentials. In several cases, I have found that the carburetors needed to be richened up about one main jet step to help smooth out the fuel delivery to the engine. I had raised the needle up one notch and was using the stock S90 main jet which was #90. With continued richness on the plug and poor performance, I lowered the needle and re-tried the engine performance once again. There was little or no change, so the main jet was reduced to the stock CL90 size, which is #88. Each time there was just a little cleaner running, but not anything that was really acceptable. Dropping the main jet to #85 seemed to be the magic setting, as the engine started to run cleaner and without the mid-range hesitation.

This may or may not be the final answer in that the air filter is a simple conical unit, standing in for the stock air cleaner/filter setup which was not available with the bike. Once the original S90 engine configuration was altered, the air filter for the S90 was no longer compatible with that of the CL90. More run-time is needed to confirm that the engine is set properly and won’t seize due to an incorrect main jet choice. Sometimes, the changes to the carburetion are masking an ignition system problem. In several cases, I have discovered that a bike will start and run at idle with a failing ignition coil, but when the throttle is cracked open a big misfire occurs and the bike fails to move forward with authority.

One of the other steps was to check the spark plug cap for high-resistance. This specific engine still carried its “Hm” logo’d spark plug cap, which are generally viewed as “non-resistor” types. When this one was checked, the resistance value measured was 33k ohms; whereas the “resistor” style plug caps have only 5k ohm ratings. Swapping out to a new resistor cap helped the performance to some degree, as one of the trouble-shooting steps. It is beginning to appear that many of these spark plug caps might well be faulty as they age and go through many heat cycles.

The ignition coils on the OHC 90 engines are mounted directly to the top of the engine cases, along with the condenser. You can check the primary winding ohms values by disconnecting the engine wiring connector plug and probing into the black wire terminal. Disconnecting the points wire connector allows for access to the other end of the primary windings set. So a probe into the black lead and one in the disconnected points wire connection will give you a reading of the primary wiring ohms resistance. If you need to service the condenser or replace the coil, the motor will have to come out again; or at least be tipped down off of the lower rear mounting bolt.

For the moment, the bike is running smoothly and may have a new owner waiting in the wings who can help take it to the next level. Given the amount of money spent on new parts to make the bike fully functional and the time invested in multiple engine work efforts, it will definitely not go down as a money-maker for MrHonda. It did provide a good platform to continue to hone my tuning skills, though, and perhaps some of these tips will resonate with my readers out there who are wrestling with similar issues. If they won’t run on the OEM spec settings… give them what they want!

Equilibrium restored, sparks recovered, pumps are pumping now...

Since the last installment, the CBR900RR carbs were re-checked; installed with rerouted emission control hoses and a new petcock/screen installed on the fuel tank. Initially, the fuel pump relay connector was jumpered to get the pump to function, but once the fuel bowls were filled, the pump slowed down like it normally does as the demand slackens. Once the bike was fired up, the solid-state fuel pump relay was re-installed on the connector and miraculously the pump functioned normally, apparently as designed. It won’t fill empty fuel bowls, but once the engine is running, the pump relay does function normally. All’s well that ends well and the bike was driven out on Sunday afternoon and apparently made the trip back to the owner’s house successfully, in one piece.

The little devil of a Sport Cub C110 was treated to another condenser, which was actually designed for a different application and a replacement ignition coil from an eBay seller. Once the flywheel was re-installed, the bike showed a nice bright spark at the coil’s wire end, but the “fits Honda CA110” eBay auction page failed to note that the spark plug secondary wire is about 4” too short. The original application was for a Bridgestone 90, which shared the same mounting points, but the primary wiring was reversed and the spark plug wire was too short for the Honda application, so it is headed back to the seller next week.

The old coil was reinstalled and suddenly was working just fine. The bike lift was lowered down so the bike could be kick-started from ground level. Initially, the bike kicked over but didn’t fire off on full choke or no choke. After using various throttle settings, suddenly it lit off and ran just fine with no unusual sounds or leaks, so success has been achieved there this week, as well.

The CL/S90 project was treated to some shorter aftermarket shocks, which required some bushing modifications, but now the rear wheel is well clear of the ground, making it sit better on the centerstand, which does have a slightly bent leg on one side.

Fitting the CL90 exhaust system to the bike left one problem which really has no easy solution. The S90 engine has a high-mounted dipstick on the clutch cover. When the CL90 exhaust was engineered for these frames and engines, the exhaust pipe runs right over the top of the dipstick handle. So in order to check the oil, you have to loosen the exhaust pipe. The normal solution, if you had a later model engine would just be to change the clutch cover to the CL90 style, but that doesn’t work here due to the different oil passages in the center crankcase that don’t match up with the clutch cover.

A few days later…

I pulled the engine back out of the S/CL90 and went forward with rebuilding it in the correct CL90 engine cases. There was a lot of cleanup to do as they had been sitting out in the open at an auto body shop gathering resident dust as well as sanding dust from years of bodywork efforts nearby. The center cases, clutch cover and dyno covers were all cleaned and flushed out in preparation for assembly with the majority of the S90 engine parts. However, there was, of course, an issue with the right side engine case where the kickstarter stopper is located. Sometime in its long life, the stopper had been sheared off inside the cases. The S90 engine was torn down and that case half taken to my good friend Rob North for some welding on the broken case half. Using the S90 case for a guide, he was able to Heli-arc the stopper back to near factory shape in the CL90 case half.

Once that was out of the way, the rest of the engine internals were swapped into the correct case set and eventually the reassembled engine was installed back into the chassis. With everything buttoned back up again, the start-up drill was initiated… and failed. Again, there was no spark at the plug nor was there a viable voltage signal at the points. I imagined having to pull the engine again to recheck the ignition coil/condenser components, but when I disconnected the point wire at the connector, the voltage re-appeared. For some reason, the old points tend to ground out at the wire connector when clamped down too hard. Readjusting the wire connector on the points brought the power back to an ungrounded state when the points were opened. With spark reestablished, the engine fired on the first kick, sounding happy and healthy once again. Now with the dipstick in the proper location, the oil can be checked and filled without difficulties.

A near-miss CBX purchase almost happened last week; but once I took a closer look, I decided to pass. The bike had 48k miles on it and the suspension was pretty loose on both ends, plus the engine had not been run for a couple of years, the tires were bald and rotten and the whole thing looked like a financial black hole. Hard for me to turn down a CBX, but I did!

Good news, of sorts, in that the grubby XL200R found a new home, basically for the cost of parts invested over the past month. That was another one of those deals best left alone in the future. Lesson learned!

The little C110 Cub is getting closer to street-legal status now. With a running engine and newly revamped clutch, all that was left were to hunt down some footpegs, which came from an eBay seller for very little money. A search back through my friend Ron Smith’s storage locker turned up a spare fuel tank and the chromed side covers for the Sports Cub so it’s looking better all the time now!

Bill “MrHonda” Silver

Delays, Frustration, Mysteries and successes… all in a week!

Wow, where to begin? First, the domestic C72 engine overhaul that was moving along nicely hit a roadblock when I discovered that I didn’t have a 250cc head gasket in stock. A quick check of eBay showed a couple of promising possibilities so I ordered one from one seller and a backup from a second seller.

First response was “I am sending two gaskets, as the OEM one has some cracks along the camchain opening area and the second one is good and flat, but is aftermarket and has some rust on the fire rings.” Those came in first and I elected not to use either one of them. The second one should have been in a day later, normally, however the tracking showed that it was sent to San Diego central office and then mis-sent to another part of the city. They finally realized the problem and sent it back to the central depot, which then sent it out to Spring Valley office. It was floating around San Diego for 5 days, including the Columbus Day holiday this year.

When it finally arrived, I hurried to open the package only to discover that the head gasket was an OEM part that fits a 305cc engine! I fired off a note to the seller, who failed to reply the first day, and then asked for more information about the gasket. After a long-winded explanation of the fact that he had listed a 268 code gasket (250cc) and shipped a 275 code (305cc) gasket instead, he came back to say that only MrHonda and a few others would know the difference; then asked why Honda would make two different gaskets for those engines!?!?!? After two more explanations about Engine Building 101 and how the fire rings needed to be close to the edge of the cylinder bore, but not within it, he finally said he would send “another one.” I mentioned that it better be a 55mm bore size and not the 61mm that I had just received and there was no active response, however a correct 268 code gasket did show up a few days later, along with another eBay purchased “backup” gasket from a seller in the Mid-West.

Once the correct gasket was obtained, another hour or two was spent on installing the cylinder head, setting the cam timing, torquing the cylinder head bolts and adding on the rest of the external accessories. Finally it is finished, but a good two weeks beyond what it could have been had the correct parts come in as requested.

Back on the XL200 bike revival, the engine proved hard to start again, even though I had it fired up with a new CDI box and other bits. The spark kept disappearing and reappearing which proved maddening after awhile. A secondary sweep of the wiring connections proved useful as there was a lone black/white tracer wire (ignition) which was found unplugged down near the steering head, all by itself. With that wire reconnected the bike fired back up on a couple of kicks and made a successful lap around the block with no issues. I finished attaching all the rest of the battered bodywork onto the chassis and it awaits a new home now. Even at $600, there seems to be little interest in it so far, but local desert season is about to come upon us, here in SoCal, so hopefully someone will snap it up for a beater bike soon.

The CL/S90 Hybrid bike was stalled out due to lack of a decent exhaust system for the early style cylinder head with the 45 degree angled exhaust port. I finally spotted an inexpensive CT90 head on eBay and bought it up for $35 including freight. It took a couple of hours of cleaning out/off the dirt and baked-on grease and oil deposits, but the valves lapped in okay and all the port configurations were just what I needed. The swap over took less than an hour and finally I had a cylinder head that would take the stock CL90 exhaust pipe that I had obtained from my friend Ron Smith. It still lacks a heat shield, but it otherwise bolted up as designed and offers a nice muted exhaust note. Interestingly enough the carburetor which was mounted on the early-style “twisted” intake manifold was a direct bolt-on to the center-mounted CL90 intake manifold, so that saved some time and effort. The CL90 carb that came with the chassis needs rebuilding, but could be pressed into service if needed. The engine fired up okay and then in the middle of warming up, just quit suddenly. The last time this happened the intake valve had a small metal fragment lodged in the seat, but this time the compression was still good. What was lacking, suddenly, was spark at the plug (a common theme lately). Checking power from the coil to the ignition points plate showed power at the connector but then not at the point wire. Wiggling and jiggling finally did something to power up the wire again and the bike restarted successfully. Unfortunately, the ignition coil and condenser are mounted atop of the engine cases, which are covered by the frame when the engine is installed. Trying to check for connections and/or a bad condenser pretty much requires an engine pull. For the moment, the bike continues to run okay, though.

Another case of spark/no spark is currently bedeviling me with the little C110 Sport Cub. There was no spark initially, so the points and condenser were swapped out. The coil seemed to check out okay with no visible issues. The wiring diagram shows the white with green striped wire that comes off of the ignition coil tying into the condenser along with the other primary coil wires beneath the flywheel.  The wire on this bike was tied to the ground end of the lighting coil instead! This didn’t seem to make sense to me, whatsoever, so I moved the wire off the lighting coil and onto the condenser junction as shown in the wiring diagrams. As with so many other Honda production runs, there were changes at different stages and two different manufacturers were used to supply ignition systems for the little Cub models.

You would think that the C100 and C110 Cub models would use the same components in their magnetos, but that doesn’t seem to be the case and the Nippon-Denso vs. Hitachi component options further clouded the picture. At one stage, I was able to get a strong spark at the end of the coil wire, but it vanished when a spark plug cap was attached.  After that, the spark disappeared completely, once again. More components are on order to see if I can finally track down the source of the voltage leaks or lack of generation of said high voltages.

A few days ago, another friend brought by a 1995 CBR900RR Sport bike which had only 2,000 miles showing on the odometer. The bike was bought at an auction in as-is condition with some rust in the fuel tank, old gasoline in the carbs and general neglect throughout. At first the carbs were brought over for cleaning, which turned out to be less of a nightmare than imagined. My friend took over the fuel tank clean up, which went horribly wrong as he proceeded with the task. After an initial acid wash, he decided to rinse the tank with water which was not fully removed afterwards. The petcock is held on a large bottom tube with a large threaded nut holding it in place. Apparently the nut was over-tightened and broke away from the petcock body.

He thought that the fuel pump was not working and bought an aftermarket replacement, which pumped like crazy and picked up the remaining water and some spare gasoline and flooded the carburetors in the process. Gasoline was coming up the carburetor vent hoses and spilling into the intake ports in large quantities. Finally, he called and asked to bring the whole bike over for me to inspect and repair.

The fuel tank was drained and left to dry in the hot sun, as-is. A new petcock, fuel lines and fuel filters were ordered, which took a bad turn when two of the three lines were reported as NLA/discontinued by Honda. One hose was tracked down on eBay and shipped in, while one of the remaining hoses was repurposed to complete the necessary connections. When the fuel tank was hooked up a jumper wire was used to prod the fuel pump into life. It responded well and proceeded to do a repeat of the carb overflow syndrome. At the same time, the new battery suddenly went from 12 volts down to 3 volts cranking, so it came back off for an over-night charging session.

The carbs came back off, fuel was siphoned from the intake ports and the emission vacuum lines/hoses were all double-checked for correct routing after the carb bowls were inspected for any signs of float valve failures. Everything seemed normal and after some rechecks on the hoses, the system was reconnected once again. This time the engine fired up with no excess fuel leaks and the engine sounded good as it ran off the jumpered fuel pump connection. Supposedly, these bikes will run the fuel pump for a few seconds, then shut down until the engine is up and running. This isn’t sufficient time to refill empty fuel bowls, even when the system works as it should. In this case, the pump wouldn’t run without the jumper wire on the fuel-cut relay connector, however once the bike was fueled and running I pulled the jumper wire and substituted the fuel-cut relay and heard the pump take off and run again. I had forgotten to turn the petcock back to RESERVE from OFF, so the pump was working hard at delivering nothing, until the petcock was switched back to Reserve. The pump refilled the carburetors then settled down to a slow and even click every few seconds, apparently as designed. So the $75 fuel cut relay purchase, which had been contemplated, proved to be unnecessary in the end.

So that’s been my week…   I hope yours was less eventful and more productive overall.

MrHonda 

Two out of three; vintage Honda bikes are runners now…

The S/CL90 project bike had gotten to a running state now, but not without more headaches along the way. Unable to find a decent point plate set quickly, a careful disassembly and cleaning of the old point plate eventually yielded a functioning unit.  The slide throttle parts didn’t seem to agree with the a/m café handlebars being used, so the old Wassel-type twist throttle was cleaned up and reused with a shortened throttle cable.

When the first attempts to kickstart the bike were made, the clutch slipped endlessly. Off with the clutch cover, checked the clutch assembly and found nothing wrong, however when the locking washer was installed below the clutch retaining nut, the outer edges of the washer pushed up against the inner edges of the clutch hub and released it every time the nut was tightened down. The immediate cure was to leave the locking washer off and tighten the nut real snugly. Once that was remedied, the engine would kick-over but still not start.

Checking the points with a test light revealed that the point wire was somehow grounding out all the time, so that was repositioned and spark returned to the plug. The next attempt at starting the engine met with limited success as soon as the engine lit off, oil started pouring out of the clutch cover gasket. The early engines have specific gaskets which I had ordered specifically for this installation, however the oil flow slot was a little too large and there was a gap at one corner allowing the oil to come bleeding out relentlessly. At least I knew that the oil pump was working well!

Some RTV in the gasket slot, left for a few hours seemed to mend the problem and the bike restarted, warmed up with no further leaks and then suddenly shut down completely. Repeated kicking did nothing for it and the plug was rechecked for spark which it had and there was fuel in the carb bowl…. So what now!!??

Checking the compression, I discovered that the readings had dropped from around 140 psi to 60psi all of a sudden. That is a good reason for the bike to quit and not restart again… So, off with its head! Somehow a tiny fragment of aluminum had gotten sucked into the intake and lit right on the edge of the intake valve seat, propping it open which caused the compression loss. Removing the tiny piece of material, reseating the valve and reinstalling the head made it all back to normal once again. Bike starts and runs well, shifts gears, stops and just needs a proper exhaust system.

The big problem for this S90/CL90 marriage is that the early S90 engines have a twisted intake manifold and a diagonal bolt pattern in the head for the manifold mounting. Additionally, the exhaust port is on a 45 degree angle vs. the later 90 degree angle for CL90 exhausts and later S90 applications. The S90 came with a short upswept aftermarket pipe and tiny rusted muffler. In order for the CL90 muffler to work on this application either the head has to be changed to the later style unit or the exhaust pipe needs to be cut and re-welded again to achieve the correct exhaust port angle. For the moment, it sits as it is while work continued on both the C72 engine overhaul and the “free” XL200 Enduro Honda which had received a new piston/rebore recently.

The XL200 engine installation went badly, at first; due to misuse of the two top engine mount bolt spacers. Swapping the spacers, which have different lengths, made the engine bolt holes all mis-aligned and it took stepping away from the bike overnight to reconsider the problem, which was pretty obvious once all the facts were considered. Swapping the spacers made the engine bolt installation easy and parts continued to be reinstalled as the afternoon progressed. Once the electrics were all connected, the engine was kicked over to check for spark… and none was noted. These engines have a CDI ignition and the spark can be hard to see in broad daylight. Even so, nothing seemed to be happening so time was taken to consult various forums and U-Tube videos trying to come up with some troubleshooting steps that were appropriate. There was voltage coming up from the stator to the CDI and readings on the coil and pulse generator seemed to be okay. CDI modules were somewhat suspect back in the early days of the technology so perhaps mine was fried. A quick check on eBay found a whole wiring harness with a CDI box attached for $40 delivered, so I took a chance that this might solve the problem. The parts came in just 2 days, but swapping in the CDI box didn’t seem to have a positive effect.

In my research, I discovered that the KILL switch is actually a continuity switch and not one used to ground out the system. The switch knob was stuck in ON position due to years of sitting outside. I was able to remove it, disassemble the contact parts, clean everything and reassemble it successfully. Once the switch was reinstalled into the system, I checked for spark once again. It is difficult to do on these bikes, as they are kickstart only and holding the plug against the head while kicking it over is a difficult chore. I wasn’t sure if there was spark or not, so I put my finger down between the plug and the head and kicked it over again…. ZING! Bingo, we HAVE SPARK now!  The KILL switch was probably all that was wrong in the first place, but that’s how we learn these things, isn’t it?

With the fuel system ready to run, spark at the plug and good compression, it should have started right up, but there seemed to be some problems getting fuel to the plug, so a little gas priming was done from the fuel bowl after the idle jet was rechecked for being clean and clear. In checking, I did discover that the two carburetor nuts were finger-tight so those were snugged up! SOMETHING worked; as the bike finally came to life after numerous more stout kicks and it settled down to a nice idle fairly quickly.  

With a live engine being fully realized, I cut a new drive chain for the bike and adjusted it up with the snail-type adjusters on the rear axle.  Once that was installed, the bike was ready for the “trip around the block” run to see if the clutch was stuck or other maladies would become apparent.  Surprisingly, the transmission dropped into 1^st gear and off I went, progressing up through each gear cleanly and smoothly. Even the speedometer was working! The only problem was that at the end of the test drive the bike wouldn’t shut OFF! Turning the ignition switch to OFF and the KILL switch to OFF did nothing to shut the engine down. I quickly removed the headlight bulb assembly and found the KILL switch wiring harness. Plugging the loose GREEN wire into a nearby GREEN wiring double connector finally killed the engine. Problem solved… or not! When I tried to restart the engine, it wouldn’t fire again until I unplugged the green wire. When I tried plugging the green wire into an adjacent double green wire connector, the engine would KILL if the KILL switch was turned to OFF, but only the KILL switch would kill the engine. The ignition switch didn’t affect it whatsoever. I think I better stay with the older bikes, where I can see and measure what is going in and out of the electrical system more easily.

The last bike on the list is the C110 Honda Sports Cub, which has a simple magneto ignition system, low compression pushrod engine and weighs next to nothing compared to the other two machines.

Well, I’ll be switched... vintage Honda ignition switches explained.

New Old Stock (NOS) ignition switches become ever rarer, as time goes on. Every so often something will pop up on a search for a Super Hawk or Dream ignition switch that is one of Honda’s many variations of a single part. This story covers the differences between the various ignition switch options on several of the 1960s twins.

125-250-305 Benly/Dream Switches

The Honda 250-305cc Dream/125-150 Benly models have numerous listings for their ignition switch part numbers, as follows; 35100-259-000 is an ignition switch assembly, but w/o the fork lock. Other similar part numbers include: 35100-202-000, 35100-212-000, 35100- and 271-000. For a full ignition switch with the fork lock, the numbers change to 35010-259-000, 35010-202-000, 35010-271-000 and 35010-272-000. The main ignition switch, used on both the 125-250 Benly and the 250-305 Dreams are electrically the same in wiring colors and functions. Benly models use a different type of fork lock than the Dreams, so that is one reason for the shift in part numbers.

Aside from the differences in the fork locks between the two models, there are two variations of the ignition switches, themselves. For the Benly/Dream models, you have the option of either a 5 position switch or a 6 position switch. New owners of these bikes often call me to ask “What are all these switch positions doing?” So, here’s the rundown: (1) Full counterclockwise position is to CRANK the engine over using the electric starter (no ignition). Next position (2) is where you normally insert and withdraw the key- OFF. Up from OFF is (3) the ON (ignition, horn, brake light, starter switch, neutral light functions) position. Next one, going clockwise (4), is HEADLIGHT ON (includes speedometer light and tail light). 

For domestic models, the #5 position turns on the little driving/parking light located inside the headlight reflector (non-sealed beam units). The last one (6) is for PARK, which turns the tail light ON and allows withdrawal of the ignition key.  Obviously, if you switch the bike OFF by turning the ignition switch key to the PARK position, the tail light stays ON until the battery dies. This is quite a common mistake made by new users of these models, so make a mental note of this if you are out hunting your first Benly or Dream.

US-model Benly and Dream bikes usually came with a 5-position ignition switch, as they all had sealed-beam headlights, so there is no room for a little driving light up front. You can substitute a 6-position switch for the 5-position switch here in the US, but for foreign markets, the 5-position switch option isn’t a good match. I do recall running across a very early Benly switch for a C90 or perhaps for a C70-75 which had no wiring for the electric starter function, which was not used in those 1958-59 versions. You probably won’t run across one of those switches very often, these days.

Dreams were not the only bikes with ignition switch options, as the CYP77 and CB450P Police bike editions had an extra ignition switch position for the patrol light function. I recently acquired a CYP77 switch which carried a 35100-282-000 part number. Ones for the CB450P models carry a -285- center code part number. These parts would seldom be found within the US, under most circumstances, although the twenty-five test unit CB450P bikes from 1965 did have limited parts support at AHMC. I owned one of those first 25 models, back in the late 1990s, and was able to order a new seat and luggage rack for the bike directly from US Honda warehouses. The CYP77 ignition switch, recently found, came down from Canada, where they did have a handful of Police models shipped for testing. When I built up my personal CYP77 Police bike, back in 2002, I was able to purchase several rare CYP77 parts from the suppliers in Canada, where the bike actually came from, as well.

Again, you can use the CYP77/CB450P switches in a standard street bike, however, you will wind up with a spare electrical switch position and wire terminal connection, unless you want to wire your phone charger into it. It is interesting that a quick search of eBay listings for Honda Dream/Benly ignition switches popped up some 6-position switches, for sale here in the US, with 202 and 271 code part numbers attached. One wonders if Honda chose to supersede the older 5-position switches with one “universal” switch, which could be used on any model. We have noticed that Honda’s release of replacement wiring harnesses for the 250-305s, all came with the “winker” wiring connections included, whereas the US-spec harnesses had winker wiring deleted originally.

S90/CM90-91 switches

A recent question, coupled with some actual hands-on experience, made me think to share some more switch information concerning the early OHC90 models.  Depending upon the application and what kind of dimmer switch is installed on the model, your ignition switch can be either a 2 wire or a 5/6 wire type. When the dimmer switch on the handlebars has just a Hi-Low beam function, the Lights ON-OFF function is controlled by the third position of the ignition switches. When the headlight dimmer switch has the ON-OFF-Hi-Low function, then the ignition switch only needs to be a two-wire type. The wiring harnesses are, of course, completely different in order to match the types of dimmer and ignition switches used.

Well, that is all there is to report on the “optional” ignition switches that you might encounter in your search for NOS electrical parts, for your Benly, Dream or S90 restoration projects.

Happy hunting and look at your potential purchases carefully.

Bill “MrHonda” Silver