Electrical tricks and tips for Vintage Hondas…

In the early days of motorcycling, Honda bikes had very basic electrical systems. However, for those of you who can fix things that you can see moving, electrical systems and components might seem like a black art where sparks and arcs are conjured up from nowhere. Let’s see if we can take some of the mystery out of Honda electrics and find a clear path of understanding where the electrons come from and go to in their various functions.

If you turn the ignition switch to ON and nothing happens (battery powered systems), then the first place to go is the battery. Lead-acid batteries require that mix of sulfuric acid and distilled water to make electricity. For bikes which have been sitting for months, years or decades, a fresh battery is the first place to investigate. In many cases, my customers bring in a bike with weak batteries only to discover that their lead-acid batteries have gone dry or at least the fluid levels are down below the tops of the lead plates. The lead plates must be fully submerged in fluid, so the first thing to do is to bring up the levels with a bit of distilled water. For batteries that have opaque cases, look for signs of the plates calcification where they have turned white along the edges. If you see that, the battery is done, so replace with a fresh one. If you don’t see the white colors on the plates, then put the battery on a slow charger, just one or two amps for a few hours and test with a voltmeter to see if it is coming back up to specifications. A 12v battery comes up to 12.6-12.8 volts when fully-charged, but they seldom maintain that level in most motorcycle batteries. A 6v battery can come up to 6.3-6.4 volts, but anything in the low sixes is fine.

                                                    Courtesy of AHMC training materials, circa 1960

If the battery seems full and gives something close to “normal” voltage, then turn the ignition key to ON and monitor the voltage with a meter. The voltage shouldn’t drop much more than a volt or two. For bikes with an electric starter, pushing the START button shouldn’t cause a huge drop in voltage. If your 12v battery plunges down to 10v with the starter cranking, then it requires replacement. If the bike has a kickstarter and the bike starts up manually, but not with the electric starter, then again the battery needs to be replaced. If the battery voltage comes up on the kickstarter function, its a good sign that the charging system is working to some extent but the battery is failing.

CAUTION: Kick-starting a bike with a failed battery and getting it to run can damage the battery and the charging system components because the battery acts as the voltage storage and regulation of the charging system. Honda didn’t use an actual voltage regulator in the early days. All you had was the permanent magnet rotor and stator, which generates AC voltage to the rectifier, whose job it is to convert the AC voltage from the stator to DC voltage to charge the battery. The fully charged battery is the source for power to the system and a reservoir for the charging system to replenish the outgoing electrons. When the battery is dead or nearly-dead, the permanent magnet charging system can generate enough voltage to fire the ignition coil and cause the engine to start up, assuming that the engine is capable of running and the fuel system is metering correctly. But the charging system no longer has the battery reservoir to store the output of the charging system and the unregulated output causes a huge spike of voltage to knock out any live light bulb that is on when the ignition switch is in the ON position. This condition can also damage the selenium rectifiers as they are not designed for huge over-voltage conditions. So, ALWAYS have a fully-charged battery in the bike when attempting to start up the engine after a long sleep. Many of the headlight bulbs for vintage Hondas are NLA and they will pop like flashbulbs if the engine is running and over-charging the system with the lights turned on.

                                                    Courtesy of AHMC training materials.

So, now that we are starting with a known, fully-charged battery, when the ignition switch is turned ON and nothing seems to be happening, first try the horn button to see if there is power to the primary system or not. If the neutral light bulb is blown out, then you won’t get an initial indication that there is power in the system. Testing the horn, will verify if there is power available or not, assuming that the horn is functioning.

If now power is indicated, then go back to the battery box and look for a single fuse or fuse block and check the condition of the fuse. If the fuse looks blown out, then there is a short in the primary electrical system somewhere. This is where some troubleshooting comes into play.

When the ignition switch is turned ON, the power comes from the battery (red wires) to the switched hot black wires that feed the major components. Those systems include the ignition system (coil and/or kill switch), the horn circuit, the neutral light circuit, and the brake light circuit. If the replacement fuse blows immediately, then disconnect the main circuits listed above and slowly connect each one back, one at a time. Often in the process of disconnecting the circuits, you may see a pinched wire or damaged connection that is the cause of the short to ground. It is a good idea to have a box of the appropriate sized fuses to use in the testing phase, however if you only have one or two, you can just touch the inner fuse block contacts together momentarily and watch for a large spark indicating that the short circuit still exists. If the short circuit has been rectified, you will see a small arc at the fuse holder, which is normal as the initial current flow will cause a smaller arc. The difference will be pretty evident. There are automatic reset fuses and test units that will open the circuit when the short exists, indicating that the fault remains, but they don’t eat fuses in the process. Once the fault is found, then the correct fuse can be reinstalled for normal operation. DO NOT install a higher amperage fuse in place of the specified one. This can cause the wiring harness to overheat and possibly cause a fire in the harness or components. Fixing a short circuit is a pass-fail result.

A basic 12v test light, found at any auto parts store is your friend in most cases of electrical problems. The will work on a 6v system, but the bulb will not display as bright as it would on 12v. Using the probe to contact various electrical contact points, the test wire with the clip goes to ground in most cases. The bulb doesn’t care if you reverse the polarity, so you can use the test light to check ignition timing by connecting the wire clip to the point wire connector and just put the probe into a convenient screw hole to make the connection function.

Some examples where things can go wrong are:

1. A shorted ignition coil 2. a shorted out brake light switch or the wiring to the switch 3. a pinched hot wire inside the headlight shell to any of the circuits that feed the neutral light wire, horn or lighting circuits and 4. shorted out tail light socket wiring for brake and running/park light functions. 5. would be any damaged or pinched harness wires 6. damaged wiring or connectors for the lighting system components.

To prevent excessive voltage into the lighting circuits, all of the bulbs in the circuit should be functioning to balance the electrical load for the charging system. For bikes that do not have voltage regulators, the charging system needs to be balanced by a fully-charged battery and all light bulbs functioning properly when the light switch is turned ON. The charging circuits only use 2/3 of the output in the normal ON position and then supply all three legs of the output when the light switch is turned ON. The light switch turns the lights on and at the same time connects the last stator output line to help balance the increased electrical load of the light bulbs. This is done through internal contacts within the switch assembly. If the switch contacts are corroded inside, then the final leg of the charging output won’t make it to the battery, and the battery voltage will slowly drop down further and further until the engine quits.

For the 250-305 Honda twins from 1960-67, there was a time where the original charging systems were apparently putting out excessive voltage and causing the batteries to overheat or boil out battery acid from the vent lines, which often leaves damage to chrome and painted chassis parts. Honda reduced the magnetic field in the rotors and created the (L) low output charging systems. The rotors were stamped with a CB72(L) markings for Super Hawks and Scramblers, while the Dreams will show a C72 (L) markings on the rotor faces. Unless all of the components are stock and functioning normally and the battery is fully-charged, often charging system issue arise on the later low-output systems. With today’s electronic options, a solid-state voltage regulator/rectifier combination unit will solve the charging system issues, as long as the stators are fully-functioning. Using these units, the stator outputs are all connected directly to the solid-state unit, which will control the charging system output electronically keeping the battery fully charged whether the lights are on or off.

     Courtesy of AHMC training materials.

The stators for 250-305s and for early Benly models have cloth wrapping around the charging coils and are pinched into the stator housing to keep them in place. After 50+ years, the insulation gets brittle and flakes off and/or the insulation gets soaked with oil by a leaking crankshaft seal. The coils need to be tightly mounted and the insulation remains intact. For small patches where the insulation has flaked away, you can use some liquid tape products to secure the rest of the insulation in place. If the coils get loose on the mountings, they will bounce up and down on the posts and short the windings to the grounded frame, which kills that portion of the AC winding output to the rectifier. Actually, when any of the three phases of the windings are grounded, basically the whole stator become grounded and fails to deliver voltage to the rectifier. When testing a stator, you want to check for continuity between all three wires, but you don’t want any of them shorting to ground. This can be tested with an ohm meter or buzz box that checks for continuity. For removal from the bike, use a heat gun to warm up the connectors, as the female connectors can shrink and hold the connectors together so tightly that if pulled too tightly, the end of the connector will come off of the wire end.

                                                Courtesy of AHMC training materials.

For most of the rest of the vintage Honda engines, the stators were submerged in the crankcase oil to help cool the windings and to prevent external damage. The coils are sealed with an epoxy that prevents damage to the coils and helps to make the engine more compact. When the dyno covers are removed to access the crankshaft bolts when turning the engine over by hand to adjust the valves or ignition timing, don’t be surprised when oil comes out when the cover is removed. You can minimize the oil leakage by putting a thin 1” board beneath the left side of the centerstand leg or foot to lean the bike slightly to the right. You will lose a little oil when the cover is removed, but it is minimized by a bit of bike lean from the centerstand wedge.

For bikes with stator connectors which are plastic 4-5 prong round or square plugs, always check the connections for any wire terminals that might be corroded or sometimes get pushed back inside the connector housing. When adding a solid-state reg/rectifier to the stator, ensure that the wire colors are a match for both sides of the connection. Generally, the neutral light wiring (green with red stripe) is packed in with the other three stator output connections and you don’t want to mis-wire the stator connector to the electronic unit accidentally.

There are a lot of aftermarket ignition switches, which may have different wiring in the connectors, so be sure to match up the wire colors whenever you change components like that.

The brake light switches are often connected to the brake pedals through an adjustable body. On some models, if you service the drive chain by pushing the rear axle back to tighten the chain, there is a chance that the brake light switch may not trigger properly. Likewise if you adjust the rear brake, that will affect the travel of the brake light switch plunger. Always check your brake light function after any bike service to the drive chain or brake pedal.

Honda 350-450 twins had a somewhat more sophisicated charging system, which includes a current regulator mounted on the bottom of the battery box. The function is to allow increased battery charge rate when the battery is low, then shunts off the excess battery current when it senses that the battery is fully charged.

Handlebar switches can be troublesome after 50 years of service and exposed to the elements of dirt, water and heat. When bikes have been sitting for many years, the copper contacts inside the switches can corrode and cause and open circuit when a function is selected. The switches can be taken apart for cleaning and wire repairs, if you use small tools and extreme caution so as not to lose the tiny screws, springs and ball bearings inside. Often the switch functions can be revived by simply cycling the switch on and off a number of times to help scrub off some of the corrosion buildup on the contacts.

The starter buttons on the early bikes present a challenge, especially if they are disturbed during a handlebar change or if the bike is involved in an accident where the switches are rotated on the handlebars. For bikes with inside the bar wiring, the wires can become grounded or sheared off when the switches are rotated. For the starter button function, the wire that come up the handlebars must be insulated from touching the handlebar hole edges or when the wire insulation gets pulled back and exposes bare wire just behind the starter button contact plate. The wire connection to the button plate must be insulated right down to the back side of the button contact plate. Exposed wire to the switch contact plate bracket will cause the starter to engage as soon as the ignition switch is turned ON. If that occurs you need to re-visit the starter button wiring and contact functions.

The left hand dimmer switches incorporate the two functions of selecting Hi-Low beam function and as a method to make the horn function. Again, the inside contacts can become corroded and/or shorted out to the handlebar ground for switches which have inside the handlebar wiring.

For those who have been doing a full restoration on your bikes with repainted or powdercoated chassis parts, you must be aware of re-establishing the ground paths for the rear tail light and headlights. Tail lights in particular require a ground for the bulb socket to the base plate, then the base plate grounded to the tail light bracket. The taillight bracket must be grounded to the fender and the fender grounded to the frame, otherwise the tail light functions will be puzzling and will not function normally.

I hope that I have shed some light on some of the basics of vintage Honda (and other) electrical systems. Wiring diagrams are available online for almost all models. See:

https://oldmanhonda.com/MC/MCWLister.php for the list of available diagrams.

Bill Silver

aka MrHonda

4/24

www.vintagehonda.com

A hectic start to 2024

It’s been difficult to find the time to update the blog page recently, due to the influx of work projects which are in progress or in a queue that continues to grow.

January began with a CL77 project that was brought in from ID for a “head gasket” and then was expanded to powdercoating, chroming and additional work that had it on my workbench for the better part of 6 weeks. After that one was completed, the same customer had brought in a CL160 for work to the charging system including a replacement stator and installation of a regulator/rectifier.

The customer hinted that one of the spark plugs had been cross-threaded which led to having to use a special thread chaser tool to clean them up enough to get a new plug secured. The old plugs had come out all black so there was a need to check over the carburetors and general tuning. For some reason, the carb needles had been raised all the way up on the last clip causing excessive richness. Dropping the needles down to the middle and resetting the ignition timing brought the bike back to normal running condition. I cautioned the owner to never remove the spark plug again as it might not withstand another plug installation on the fragile threads. That was another week plus on the workbench.

With these bikes in progress, my friend Don brought over a 1963 C105T bike that had a broken kickstarter shaft. That requires a full engine tear-down to replace. I had to dust off my thinking cap to recall all the steps to get the cases apart and back together again. The cylinder head valve seats were rough but I eventually got the valves to seat properly. The carb slide was jammed in place and required some head and chemicals to remove. The only replacement slide I could find was a used one, but it was better than the one that came out. Again, the specific carb kit for the C105T was difficult to obtain.

The chassis needed all new cables, which were ordered from Thailand, so the chassis went back to Don, while I finished the engine. But that was just the beginning of the month’s adventures in Feb.

Another of Don’s customers wanted an SL90 restored, so he dropped off the bike and I pulled out the engine for a rebuild. It was covered in greasy mud which proved difficult to remove and cleanup. The engine turned out to be a hybrid modification including a big bore piston, stroker crankshaft, and racing cam all installed in a bike with the stock carb and exhaust system. That story will be detailed later on, when the bike is complete.

In March, my friend Bill asked if I could “reassemble” a CL175 engine, which had been disassembled for a restoration project that never was completed. I had already sent the C105 engine back to Don and the SL90 engine was on my little push dolly, so I cleared off the workbench for the 175. The engine arrived in a wooden crate that took about 15 minutes to disassemble. It turned out to be just the bottom end with a damaged kickstarter shaft, so that one needed to be torn down as well. I had the top-end parts vapor blasted, rebuilt the carburetors, installed the new kickstarter shaft and rebuilt the cylinder head with new valve stem seals. The cylinder bores were still STD but there was some water damage farther down the bores. I bought a ball hone and worked on the bores to the point where they seemed usable, so I bought a set of STD rings and eventually reassembled it, bit by bit. The gasket kit provided was marked CB175, but turned out to be a CB200T kit with the wrong head gasket and point cover. I had to reorder a correct head gasket and then the rings took a long delayed tour from KY to OH to NY and finally to the west coast to San Diego. It took 10 days for the rings to arrive.

In the queue are the following customer requests:

Customer #1

CB77 (my ex bike) and a CL77 for repairs

Customer #2

CB77 and CL77 for repairs

Customer #3

CA77 for tires and leak repairs

Customer #4

CL72 top-end overhaul

Customer #5

CL77 head gasket

Customer #6

CB750 oil leak behind the ignition

Customer #7

CT90 oil leak at base gasket

So, I apologize for the lack of blog stories, but there are a few more stories in the works, coming soon. Thanks for reading the old ones and your support for the blog page.

Bill Silver

aka MrHonda

www.vintagehonda.com

4/19/24

NOTE: All photos are courtesy of American Honda Motor Corporation

 Fluid management... Rainy day musings…

                                              Smiley face, about to be erased on the fuel lever.

Honda kept from going with liquid-cooled engines until the GL1000 Gold Wing in 1975. Soichiro was so adamant about keeping engines air-cooled that he had his engineers design a air-cooled four-cylinder 1300cc car engine for the model called the Honda 7/77 or just the Honda 1300.      see: https://en.wikipedia.org/wiki/Honda_1300. Beyond the Gold Wings and the following CX500-650 V-twins, liquid cooling slowly seeped into mainstream motorcycling with each model year. And with that, coolant leaks began to show their nasty selves.

Honda’s reputation for cleanliness in designs and functions is legendary. Vintage Honda motorcycles from the 1960s-70s are not supposed to be dripping fluids beneath the machine if normally maintained.

Apart from chain lube being flung off the chain at both sprockets, Honda machines should not be drooling anything else. Of course, these 50-60-year-old motorcycles have aging engine oil seals and gaskets which are typically the sources for any oil leaks. What are the fluid sources?

1. Engine oil, leaking from oil seals and gaskets and sometimes from breather tubes when the engine is tired. Honda used the stud channels in the cylinder and cylinder head to feed oil to the camshaft, rockers, and tach drive hardware. The gaskets generally have an o-ring placed inside the oil feed hole to prevent oil migration through the gasket material. What seems to be a good solution often fails as head gasket oil leaks are prevalent on almost all models of air-cooled engines. Heat cycles, hot oil, and expansion of the parts, sooner or later will reveal oil leaks that migrate past the sealing o-rings and laterally through the gasket material. Forgetting to use a new drain plug gasket often results in a small oil drip beneath the engine. BTW Honda 160 engines have TWO drain bolts.

2. Fork oil, from leaking fork seals, of course. This wasn’t a problem for most models with leading-link suspensions, but they did have small, ineffective dampers shoved up inside the pressed-steel fork housings that could eventually leak the small amount of fluid inside. Honda’s early design shocks had replaceable shaft seals, but later they just crimped the seal housing into the body, negating any service attempts.

3. Battery acid! It’s hard to find a nice clean vintage Honda that doesn’t have signs of battery acid leaks onto the frame or mufflers. Either the vent tubes fell off from vibration and age or people forgot to hook them up when the battery was removed for service or replacement. Today’s new AGM and Li-On batteries have no fluid openings to leak, unlike the classic lead-acid batteries that we all grew up with in the 1960s-70s.

4. Gasoline. Starting with the top… the gas cap. Early gas caps used a simple baffle system which featured a small vent hole to allow air to help vent the fuel tank properly. This prevents air locks in the fuel system, however, it also allows evaporating gasoline vapors to leave the tank, eventually causing a buildup inside the tiny 1/16” hole which creates a vacuum in the tank. The early gas cap gaskets were made from cork and degraded quickly due to the compression of the spring-loaded cap retainer mechanism and exposure to gasoline products. Bad gaskets, caused fuel leaks at the top of the fuel opening, especially with a full tank of gas. Honda replaced all the cork gaskets with modern rubber compounds that resist breakdown from fuel exposure and cap spring tension. Having a lap full of gasoline when you hit the throttle or brakes with a full tank is downright dangerous, if not very uncomfortable when it seeps into your crotch area.

Fuel leaks can occur in many places in vintage Honda bikes. Besides the gas cap, the next step down is the petcock/shut-off valve. Most of the early models used a rubber 4-hole gasket to seal against the fuel selection lever face. Either the 4-hole gasket degrades and starts to leak around the lever arm, or the back side of the lever has both warped and become etched with gasoline acids, causing fuel to bypass the lever setting, even when OFF.

The lever face can usually be smoothed out with a fine-cut file or piece of high-number grip wet/dry sandpaper. That step, coupled with a new 4-hole gasket, should fix any petcock leaks at that point. The other fuel leak source at the petcock is where it attaches to the fuel tank. CB72-77 and most of the 350-450 lineup used a large nut that has left-handed threads on one end and right-handed threads on the opposite end. There is a thin rubber flat gasket that is supposed to be squeezed down when the petcock is secured to the fuel tank nipple evenly with the threads on the petcock body. If one end bottoms out before the other, then the petcock will be loose and often leaking.

For petcocks that bolt to the bottom of the fuel tank, either with one or two screws, you MUST use the proper sealing washers on the screws to prevent fuel from seeping down past the threads into the fuel cup. Be sure that the screws are tightened securely to prevent leaks. Also, replace the o-ring that seals the body to the tank on these models. Otherwise, the same cautions are true for the fuel lever and 4-hole gasket.

Most early petcocks used a long brass tube to feed fuel to the carburetor when in the ON position. When the fuel level drops down below the tip of the fuel tube, then turning the fuel lever to RES is required and allows you to use the remaining fuel below the brass tube to help you make it to the nearest gas station. After 50-60 years, the brass tubes will suffer cracks or become plugged up. In years past, when petcocks were cheap, you just put a new one on. Petcocks for CB72-77 and CL72-77s are becoming very scarce, so the fix is to remove the old fuel tube and replace it with a section of 5mm brass tubing which can be purchased from hobby stores or online. Clean out any remaining debris from the tube hole and then just tap in the new section. Now you have the RESERVE function available, once again.

Often, when old fuel lines are left connected to either the petcock or the fuel fitting on the carburetor, the brass fitting pulls out of either part along with the fuel line. Carefully, cut the old fuel line off of the fitting piece and tap the brass fitting back into the hole. The end of the brass is somewhat tapered so usually will bottom out securely into the hole and stay secured.

Carburetors, of course, have the task of metering fuel in the correct amounts at various engine speeds and throttle openings are full of fuel and the potential for fuel leaks.

The early 250-305 Honda models used a banjo fitting and screen bolt to allow fuel lines to be attached to the carburetor bodies. The banjo fittings, not unlike those on the master cylinders of bikes with hydraulic disc brakes, need washers on both sides of the fitting. Fiber washers were used for many years, but then aftermarket makers started using punched-out aluminum washers which deform enough to seal fluid leaks. Most of the rest of the vintage Honda models used pressed-in brass fittings which generally give little cause for concern.

When carburetor float valves stick open due to dirt, wear, or the floats dragging up against the bowl gaskets, the fuel will leak out through the small brass overflow vents. When carburetor bowls begin to leak at the bottom of the overflow tube and all else has been replaced or cleaned, look carefully at the brass tube inside the float bowl. In many cases, the fuel tube has cracked down the side and is slowly draining the fuel bowl. You can often either use a good quality soldering iron and solder up the crack on the outside or slip a piece of 4mm tubing over the outside, secured with JB-Weld or a good epoxy adhesive sealer.

Most float bowls have small drain plugs at the bottom. Loosening the plugs can drain the bowls out without complete removal. Because water often works its way into the fuel system, the water sinks to the bottom of the bowl and often causes corrosion between the drain bolt and bowl threads. Also, the drain bolt requires either an o-ring or flat gasket to seal it to the bowl.

Carburetor float bowl gaskets are another source of fuel seepage. Once the bowl is in place, the fuel level is near the top of the bowl and will leak out the front side of the bowl/gasket area if the gasket is not correctly made, the bowl clip doesn’t have sufficient pressure to clamp the bowl securely or there is leftover gasket material in the body, itself. Honda used some kind of magical adhesive to glue the bowl gaskets in place originally. When the gasket is cracked and leaking, you have to clean the gasket channels very well to prevent any leftover stray bits to prevent proper gasket sealing between the bowl and gasket. Check the edges of the float bowl for any leftover debris or if there are irregularities to the edges of the bowl surfaces.

Honda’s bowl gaskets for 1960s models are about 2.5mm wide. Many of the aftermarket kit gaskets are 3+mm wide and do not lay flat on the front edge of the carburetor body. This has been a problem for many years, unfortunately. In some cases, use a small hand-held hole punch to notch the gasket where it contacts the two small posts in the carb body gasket channel.

Other places…

Leaving your bike out in the rain, or stored for long periods where the tire tubes deflate, allows moisture to seep in between the rim and the tire bead, causing rust and corrosion to build up on the inner rim surface and ends of the spoke nipples. Any tears in the seat upholstery will allow water to seep into the foam and eventually settle down into the metal seat pan causing rust and eventually holes in the steel seat pan material.

Early model instruments don’t really have a way to vent out moisture inside the unit. When bikes are left in the rain or even fog, after a ride, the moisture inside the meter will condense and a layer of moisture will form on the inside of the meter lens. In a worst-case scenario, the moisture will get into the speedometer mechanism itself, damaging the odometer number strips and the magnet and little gear train inside.

Stay alert for fluid leaks of any kind and mend them early to prevent mishaps or just an ugly motorcycle appearance.

Bill Silver

aka MrHonda

1/20/24

Miss and match… CL72 vs. CL77 Honda Scramblers

There are a lot of misconceptions about the possibility of interchanging parts between the 250 and 305cc Scrambler models. I thought I would take a few moments to help clarify some of the interchangeable parts and those that are not directly able to be swapped out.

1. 305cc top ends on 250 engines.

The upper cases of the 250cc engines do not have sufficiently enlarged bores for the 305cc cylinders. To make a 250 into a 305 you generally have to bore the cases out to fit the 305cc cylinders and sleeves.

Adding the 305 top end will change the balance factor on the engine, as the 250 crankshafts have a different balance factor than that of the 305 engines. Bottom line: It will probably vibrate more than it would as a stock 250cc machine.

2. Cylinder heads

While the cams, valves, springs, and rocker arms are interchangeable, some of the cam sprockets might not be the same due to differences in the camshaft and sprocket spline configurations. The 305 cylinder heads have an enlarged squish band to allow the jump from 54mm to 60mm pistons to clear the combustion chamber edges. Note that the head gaskets have fire rings that are either 55mm for the 250s or 61mm for the 305 applications, to allow for use of up to 1.00mm oversized pistons and rings.

3. Carburetors

The switch from 250 22mm carburetors to 26mm 305 carburetors requires matching carburetor insulators and o-rings. The intake ports on the 250s seem to be a bit smaller than those of the 305 heads.

4. Throttle cables

The standard 273 code throttle cables are manufactured to match the height dimensions of the 22mm carburetor slides. If the 273 cables is used on the 305 CL77 carburetors, there is a chance that the slides will not be raised fully. Conversely, the later 305 throttle cables have split ends which have excessively long cables to the carburetors, so that you wind up with excessive cable slack that can’t be adjusted out with the cable adjusters on top of the carburetors.

5. Carburetor calibrations.

The stock main jet for the 305 CL77 carburetors is a #130 with a #38 idle jet. 250 carbs are going to see main jet sizes down to about #120-125 with #35 idle jets. The slide needles have different tapers from those on the CB carburetors, which will interchange with the CLs if the correct calibration parts are used. The round bowl carburetors can use the later square bowl floats, which have been superseded to the 286 parts from the 250-350 twins from 1968-73. Even the needle jets are of different sizes and part numbers.

6. Engine swaps

There is no physical difference between the 250 and 305 engines, so swapping out a 250 engine for a 305 is a straightforward proposition. However, the top covers on the 250 have solid bores for the engine mount bolt, whereas the 305s have a rubber cushion inserted into the cover

7. Engine changes

Honda revised the spline depth of the transmission and even the crankshafts in the later days of production. The later splines are shallower, which can be used on deep spline shafts, but not the other way around.

8. Cables

The switch from “small brakes” to “big brakes” necessitated changes in the brake cable dimensions as the reach from the backing plate to the brake arms is different. This applies to both front and rear brake cables, thus the change in the part numbers after about the 15k serial number series. The early cables with the big chrome adjustment knobs were superseded with standard CB72 lever brackets and adjusters and a CB450 brake cable, with a CB175 clutch cable.

9. Exhaust systems

Original 250 exhaust pipes were straight back with little baffles tucked in, flush to the ends of the pipes. In 1965, with the release of the CL77s, the exhaust notes were dampened down by the use of a slip-on rear muffler that joined both pipes together at the back. Each exhaust pipe still had individual baffles but the ends were extended past the pipe's terminations and the baffles were retained by headless bolts that were screwed into self-locking nut plates. As these were easily removed, Honda switched up to a muffler which was welded onto the upper pipe with the lower one sealed by a packing sleeve and a clamp. An additional baffle was installed inside the muffler body, as well.

10. Seats

CL72s and early CL77s used a double, metal-to-metal, fork mount on the front of the seat pan to connect it to the frame. To reduce the vibration being transmitted into the rider’s body, the seat mounts were rubber mounted with a U-shaped rubber mount up front and rubber cushions at the rear mount legs. Obviously, the frames had to be modified to conform to the front seat mount change.

11. Forks

Despite the use of the same fork bridge and stems for all models, the forks, themselves, were drastically different, and different versions of the fork boots were employed. Later model fork ears were also rubber-mounted and required an additional pigtail ground wire to allow for the full function of the headlight and instrument lights. The Type 2 alloy forks were employed on CL72s after 1008551, but the CL77s had the change just shy of the 15k serial number mark. Steel fork cases can be damaged if the original length fender mounting bolts are replaced with longer ones than specified.

12. Rubber mounts

Honda’s quest to reduce rider fatigue and component failures due to excessive vibration resulted in the rubber mounting of the seat, muffler, fork ears, and rear fender.

13. Ignition switches

CL72s used an ignition switch which was almost identical to the CB72-77 switches, except the threaded portion was extended so that the outer side cover latch to be attached. Later CL72s and all CL77s used the two-piece ignition switch mounting and switch assembly, thus the frame mounts are different between the two styles.

14. Wheels and hubs

The switch from small SLS brakes to the big 200mm DLS brakes required new hubs, spokes, and brake components, as well as the rims. All CL wheels are 19” but the spoke angle changes when the hub sizes are increased, so not only are the rims different widths between front and rear, but the spoke holes are angled differently so the spokes can reach the hubs properly.

15. Rear Suspension

The original early CL72s had double-eye shocks, which were replaced with eye-clevis by 1964 All CL77s had eye-clevis shocks. The early rear swing arms were machined to hold the sprocket carrier on one side, allowing the rear wheel to be removed without disturbing the drive chain. The swing arms, chain adjusters, and all of the mounting hardware for the early machines didn’t work for the later rear hubs, which were CB-based and used CB rear sprockets.

Bill Silver aka MrHonda 

www.vintagehonda.com

www.mrhonda.guru blog site for more stories.

MrHonda takes a ride on Chinese Junk…

Finding functional parts for 50+-year-old Hondas has become ever so difficult as the years go on. Simple parts like points, condensers, rectifiers, and fuel system components are all long gone from Honda’s warehouses and dealerships.

Aftermarket parts have a rather poor reputation for quality and accuracy. While most of the replacement parts come from SE Asia (Thailand, Taiwan, Vietnam, Hong Kong) more and more are being filtered in from Chinese companies who try their best to copy the original OEM parts but don’t quite have it right in many cases.

The current example brought to me was a tidy CB160, which had some restoration work and was showing low miles on the odometer. The overall look was very presentable, including nice OEM mufflers on both sides and a set of Hedenau tires on both ends. The owner had seen my name on various forums and noticed that I was in the San Diego area. He lived in Escondido, which is about 40 miles north of Spring Valley, and contacted me to see about getting his “carburetors” rebuilt.

                                                Sweet bike with optional rear rack/

Having just cleared out a set of CL77 and CB77 bikes from an owner who also lives about the same distance away, just in a different direction, I was able to take the CB160 in for some needed repairs.

The owner brought it down in a U-Haul motorcycle trailer, hauled by his late model Ford Crew Cab truck. The bike looked very nice at a distance, but as we removed it from the trailer I noticed something that was definitely out of the ordinary… The carburetors were Chinese copies of the early Power-Jet CB/CL175s from the 1967-69 era. The owner had purchased carb kits for a “CB160” in hopes that they would be useful for the repairs. The petcock had an additional shut-off valve plumbed into the fuel delivery system, all of which was done cleanly, but eventually not necessary.

The previous owner stated that he had tried to repair the petcock and it kept leaking, thus the installation of an additional shut-off valve. Apparently, the petcock leaked into a carburetor, which filled up and flushed fuel down the intake port and into the crankcase. Rather than just flushing the gasoline out with a couple of oil changes, he decided to rebuild the whole engine! Once completed, it went up on BAT (bringatrailer.com) for sale. And now it was in San Diego with a worried new owner.

So, the first order of business was to see if it would start, giving me a few clues about what the issues were. The nice hot battery kicked the engine over but with a skip and clank sound due to the starter clutch springs being worn down. The bike had been sitting for a few months, so I surmised that the fuel had gone off and the idle jets were plugged.

After removing the side covers, air filters, and carburetor set, the carbs were disassembled and inspected. Sure enough, the idle jets were blocked. What I have seen consistently is that the Chinese carburetor manufacturers fairly accurately copy the original Keihin designs but take some liberties with some of the components and also completely fail to mark any of the jets or needles with any kind of calibration clues. So, with basic cleaning and unplugging the idle jets, I checked the float level settings against the Honda tune-up book. There are two different float level settings for the 160 carbs but only one for the 175… 21mm. When I went to measure the float height, they seemed to be about 21mm but the flange where the gasket sits was raised up a couple of millimeters, so if you measured at the gasket surface area, the reading would have been more like 24mm. Both carbs were the same, so I left them as manufactured and waited to see how the engine would perform. The carb slide needles were also unmarked, but the clips were set at the #2 slot. The owner complained about the engine not taking the throttle cleanly, so I moved the clips down to the #4 slot and reassembled everything after changing out the o-rings and bowl gaskets.

This brings up another annoyance… The width of the bowl gaskets is usually too wide and the front section hits the two little posts that are supposed to keep the gasket from pushing inwards when the bowl is attached. What happens is that the gasket starts to flip upwards until it is compressed by the edge of the float bowl. I have started using a small hand-held punch to notch the gaskets where they are supposed to ride up against the posts, to help keep the gasket flat in the track.

The other issue, at least for CA owners is that all the pump gas has 10% alcohol which causes the rubber bowl gaskets to expand and distort when exposed to these fuels. Often, when you remove the float bowl to service a jet or check the float level, the gasket expands out beyond the original size and it will NOT go back into place. It has become necessary to keep extra gaskets on hand to use when the originals cannot be installed again. Fortunately, some of the gasket makers are now using materials that are alcohol-resistant but they still make the widths excessively wide in most cases.

The carburetors continued the dance, each doing different things. One would leak past the bowl gasket in front. The edges of the bowls were machined off with something rough so there were a series of gouges in the edges. I filed them down as much as possible and finally, the gasket stopped leaking. Then the other one started overflowing. The floats are plastic and I was concerned that one might have leaked internally. I finally used the float valve from the kit, which uses a different type of needle, but it worked and the fuel stayed inside for both sides, finally.

                                            Chinese copies of early CL175K0 carburetors.

The petcock problem was that it was dripping with the lever in the OFF position. I drained the tank through one of the fuel lines and then pulled the lever plate off with the 2 screws. The 4-hole gasket was in poor condition and the back side of the lever was cupped at the edges. I smoothed out the lever face, installed a new petcock gasket, and buttoned it back up. When I added the ½ gallon of gas back in, the petcock started dripping again! I drained the tank again and rounded up the parts from the supplied petcock kit to remove it and determine what was happening. With the bowl off, the screen, and the o-ring removed, I put a screwdriver on the first screw and it was loose! Even though the previous attempt at kitting up the petcock failed, the actual reason was that the screws were not tightened securely and the gasoline was draining past the screw threads and filling up the bowl directly, bypassing the fuel valve.

I replaced the aluminum screws with some fiber washers from the repair kit that came with the bike and suddenly there are NO drips from the petcock now. Problem solved and all the extra plumbing and shutoff valve stuff was discarded for a couple of nice chunks of Honda 5.5 fuel line of matching lengths. This brings up another subject…

Any of the vintage bikes with dual carburetors can be subject to fuel starvation on one carburetor, even when the petcock is clean and the float valves are working normally. What seems to happen is that the fuel flows to the easiest pathway and air seems to be trapped on the opposite side fuel line. Some people have tried blowing into the gas cap opening to pressurize the fuel lines which sometimes works, but is NOT a recommended practice. What I have suggested to others and what I have found is if you use matching lengths of fuel hose to each carburetor, the problem disappears. At least that has been my experience to date.

So the next round of repairs was to address the slipping starter clutch. I had forgotten that the little twins use a 15mm release bolt instead of the commonly used 16mm size. I dug through my selection of axles and found one that worked perfectly. Once the rotor was removed, all of the rollers were still in place with some spring pressure, but when they were all removed, the lengths were just under one inch and the new ones were about an inch and an eighth. Doesn’t seem like it should matter much, but it usually does fix the problem. Getting the rotor back in place was a bit tricky with the side cover still in place. I lined up the crankshaft locating pin with the rotor and held the rotor squarely on the end while I reached over and turned the crankshaft with the kickstarter arm. It took a couple of tries but you can generally nudge them back in place without removing the whole surrounding cover. The starter function was much improved, but it still had a little bit of slip, probably due to some glazing on the starter clutch hub surface.

After all of this work, the engine spun over with the electric starter, but wouldn’t fire up. I pulled the plugs and they were fuel-fouled, so I connected a fresh pair to the plug wires and looked for spark. It didn’t seem to be present. Off with the point cover and when I arced across the open points, the plugs fired, but not when it was spinning over with the starter. The aftermarket points seemed to have been corroded over which failed to allow them to close correctly, so there was no current flow through them to energize the coil windings. A bit of scrubbing with a Dremel cutoff wheel disc and some contact cleaner and we had spark once again. I checked the ignition timing and it was right on the F mark, so it was good to go.

The bike fired up on full choke but didn’t want to run with anything less than it full on for about a minute. These carbs do have the little spring-loaded flappers which prevent over-choking the engine. After a minute or so of choking, it finally took throttle correctly. I’m sure that the needle clip position had a lot to do with early running issues, as the primary problem.

Then, there was a problem with the oil change… The 160 engines have TWO drain plugs underneath and the forward one had a 14mm head bolt instead of a typical 17mm bolt head. When it was removed, the “drain bolt” turned out to be a shift drum locating pin with the roller still attached! I had to check the existing one to be sure that someone hadn’t accidentally switched places, but it was correct, so I guess the forward drain bolt was lost and the owner just used whatever fit in its place. I do get the weird ones lately.

NOT a drain plug

I had to air up the tires from 15psi to 30psi before a test ride around the block and down my little testing route. The bike pulled third gear up to 50 mph on my uphill road section and sounded great.

I called the owner and said “Come get it” and he happily came back down and loaded it up after a bit of a test run himself to see how my work had transformed the reluctant starter machine into a fully functional one, once again. After all was said and done, he mentioned that he might sell it because after fulfilling his childhood memories of owning one, back in the 1960s, it was now really too small and under-powered for general use. I hear that a lot from owners who want to relive the past for a moment, but then the reality of regular use sets in.

So, now back to the current CL77 project, which arrived in the back of a mini-van, mostly in pieces.

Bill Silver aka MrHonda

01/2024