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Another demon CB350 comes my way…

The 1969 CB350 is a one-owner bike, with 13k miles showing on the odometer. It has been lovely cared for by its 75 year old owner, who loved to take it to the local summer car shows in El Cajon, CA and show off its originality and patina to admiring onlookers. My friend Scott, who attends these meets regularly, started up a conversation with the owner, Cal, about a year ago. Cal had issues with the bike like stalling unexpectedly and difficulty getting it into neutral with the engine running. He had taken it to several independent shops, where they overhauled the carburetors and replaced the outer engine cover gaskets (recommended by Honda). Still, the problems persisted and Scott told him to contact “MrHonda” for some more expert opinions and possible repairs.

MrHonda is not all that keen on doing repair work on the 350s, due to odd engineering issues, accessibility to some components and a history of spending way too much time on “simple” problems which wound up costing a lot of $$$ to finally resolve (or not, in one case). The bike’s throttle response is somewhat sudden on and off the throttle. The remote shift linkage mostly came from the CB77 Super Hawks and the clevis ends and pins wear out leaving a lot of unnecessary slack in the shifting mechanism. Engine vibration reeks havoc on chassis parts, including the batteries and mufflers. The fuel tanks have the dreaded crossover tubes which always spills gas all over the engine, during removal. There are a lot of gaskets, o-rings and seals which can leak over time, plus the charging system components can be problematical.

After a phone conversation discussing the various issues, the bike was brought by the house for inspection and repairs. When riders complain about shifting issues, when trying to select neutral, the cause is generally in the clutch. Poor adjustment or worn components cause the clutch plates to drag sufficiently to put torque on the transmission gears enough to prevent easy gear selection. So, the first thing was to drain the oil and remove the clutch cover (after loosening the footpeg bar and muffler). The clutch cable adjustment procedure requires loosening the locking nut and turning the adjuster screw counter clockwise until it stops, then backing the screw off about 1/8 to ¼ turn, then locking down the nut again. With the clutch cable adjusted properly, turning the engine over with the rear wheel, when the transmission was in neutral and clutch lever pulled in, there was some irregular motion going on with the clutch pressure plate. It was evident that the clutch was not disengaging cleanly due to a warped pressure plate. MrHonda’s shop doesn’t usually store Honda 350 parts, but looking at the pressure plate reminded one of those used on the 250-305 engines. Digging out a decent CB77 plate, it was apparent that the four spring holes were a match to those of the 350, with some detail changes here and there. When installed, the cover did not appear to have the same kind of warpage of the original part, so it was cinched up and the clutch cover reinstalled.

When Cal dropped off the bike, the first thing to show him was the tiny little vent hole in the gas cap, which is nearly a match for the 250-305 twist caps. Years of debris and varnish had all but plugged up the vent hole and it was a near certainty that this was causing his stalling problem.

Supposedly, the carburetors were overhauled and that is often a “red flag” for me because shops often order up Keyster carb kits which do not have all the correct jet sizes for the 5 different calibrations for these carburetors. With the fuel tank removed, the carbs were pulled off, after the air filter system was dismantled. WARNING! Just about any time you remove the float bowls of the 350 carburetors, the bowl gasket/o-ring will swell up from the alcohol in the gasoline and you will NOT be able to reinstall the bowl again with the old o-ring. With the bowls removed, jetting was checked against the carburetor calibration code stamped on the carburetor inlet web and in this case the jets were correct originals. The float level was about 2mm lower than the specified setting, so that was adjusted. All passages were cleared with jet reamers and carb spray. One float bowl gasket stayed in place long enough to be reinstalled, but the other one had grown about an 1/8” and was not going back together without a fight. One solution is to simply pack the bowl lip groove with silicone grease and squeeze the o-ring back into place and then quickly install the bowl. When the o-rings are way too far stretched out, then a razor blade trim job will shorten it back up to the necessary size. With carbs back in place, and fuel tank reinstalled, use of the electric starter yielded a spinning engine but no running until the starter button was just released. This condition occurs when the battery voltage (in this case 11.65v) is too low and cranking on the starter motor draws it down even further, robbing the ignition coils of sufficient voltage to fire the spark plugs.

The bike did kick-start okay, but ran rough and didn’t take throttle very cleanly. Further investigation of the ignition points showed the gaps to be just at the minimum of .012” When the point gaps are reduced to that level, then the possibility exists for both sets of points are “sharing” voltage/current for a moment, which reduces the coil energy considerably to both coils. The spark advancer unit return springs were somewhat slack, which can cause inadvertent spark timing advance at idle. That condition will cause the engine speed to rise up unnecessarily which cannot be controlled with the idle speed screws in extreme cases.

In going over the engine, normally a check of the camchain tensioner is included. When the tensioner was inspected, it was a shock to discover that this engine still had an original “hydraulic” tensioner, which Honda superseded to the spring-loaded manual tensioner not long after this bike was built. My friend, David, who is parting out a CB350 offered up an inexpensive manual tensioner from his parts bike, so all that was left was to remove the old one and spend about 20 minutes carefully scraping off the 45-year old gasket from the back of the cylinder block. Eventually, the task was completed and the manual tensioner was installed successfully. I think that the hydraulic tensioners didn’t keep tension on the camchain for a few moments, until the oil pressure built up to apply juice to the tensioner piston. For that and perhaps other reasons, Honda started using mechanical tensioners on the rest of their production of CB/CL and SL350s.

After all the final adjustments were made, the bike was taken out for a test run. There was a jerking, push-pull sensation in 3rd gear that, at first, felt like a slipping clutch. Having already been into the clutch assembly and cleaning off the steel plates with a wire wheel, I was certain that the problem did not come from a “slipping clutch.” Strong acceleration in the lower gears was good until 3rd gear was selected, then it started the jerking action, but only in 3rd gear. Relaying the information back to the owner, he felt that his clutch adjustment effort had gone wrong and that the clutch was slipping and the problem was there and not with the transmission.

The clutch cable was the original one; cracked and worn. I offered the solution to replace the cable with an OEM Honda cable, from the dealer, but all the current ones are made of black sheathing and his cable set were still the original gray/silver versions. Searching the internet yielded an aftermarket silver cable from a seller in PA. It was listed as a “replacement” for the Honda 350s. It was just a few dollars, so it was ordered with priority mail shipping. SOMETHING went wrong and the cable wasn’t shipped for a few days after, so the bike sat in the driveway. One correct-style cable was fished out of the cable bin, but it was about 6” too long. It was connected anyway, just to see if some of the shifting problems were cleared after the clutch repairs, but the extra length was too much for a normal function, so was removed and the bike covered up until a proper cable could be sourced and installed.

When the cable arrived, the length was about 4” too long, so I hauled the cable up to a shop, fifteen miles away, who will make new cables or cut down ones like this one. After an hour’s wait, the cable was done with a new fitting soldered onto the bottom end of the inner cable wire.

With the cable installed, the bike was tested again and the owner called to pick it up. I had road-tested it before I called him and it seemed to be functional. Cal got just 4 blocks before the top fitting on the cable snapped off the cable wire! He called and I went up, nursed the bike back home and then took him back home, another 15 miles away. A “Motion-Pro” cable had been ordered as a “back-up” in case the a/m silver cable didn’t work out. It, too, was delayed in shipping for a few extra days, even though the seller was less than 100 miles from my house. When the Motion-Pro cable arrived, it too was about 4” too long, so was wrapped back up and set aside.

An eBay seller claimed to have an OEM NOS Honda cable that would fit the CB350, but the “Buy it Now” price was $54 with free shipping. The seller was in Rhode Island, however, so it was going to be another couple of days before it would arrive. The seller sent a “shipped” notice on Thursday with tracking. On Monday, the tracking number was checked and revealed that the cable had just been shipped that day, not the previous Thursday! A note to the seller finally revealed that his mailman had not picked up his outgoing mail for 3-4 days, so it didn’t get out until Monday.

FINALLY, the cable comes in and it is the right length, color and type, so it is installed. The bike fires up easily, after its newly-charged battery is put in the battery box. The engine starts right away with a little choke and the electric starter. With a short warm-up, the bike rolls down the street feeling like a “normal” CB350. Cable feel is good and finding neutral from 1st or 2nd gear was easily achieved. The only big issue is the 3rd gear jerking condition, which fitting the new cable to the engine did not cure. The only “cure” for that symptom is to tear the engine out of the chassis and split the cases to access the transmission and shift drum/forks.

Fortunately, Cal has decided to just take the bike with current improvements, and just ride it easy for awhile. Personally, I really don’t want to tackle another CB350 engine teardown, anyway, so we are both happy to call a halt to the proceedings for now. Hopefully, that is the last I will be seeing of the troublesome Honda 350 twins around my shop for a good long time. Apparently, this one was a cable-phobic as all of the attempts to receive a fresh, correct clutch cable were divinely diverted OR the whole bike is cursed with even more gremlins yet to be discovered.

Bill “MrHonda” Silver