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