Technical Q and A for classic motorcycle maintenance and repair.
Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.
Q: I’m hoping you can help me with a couple of problems we are experiencing on our newly restored 1968 Yamaha YR2C. My son and I completely rebuilt this bike and we are experiencing a problem with the clutch. Everything within the clutch was in good shape; the plates measured up as new and the basket and bearings were good. We installed NOS (new-old-stock) springs in it, a new cable and a new release mechanism as we found out the original was cracked. The NOS replacement release mechanism came cracked as well. The cracks in it were minor compared to the original. The problem we are having is that the clutch is very heavy to operate and after a few miles it hurts your hand to use it. As mentioned, we put in new springs, but that didn’t help, and a new release mechanism. We have all the correct spacers, plates, O-rings, etc. We adjusted it per the manual, but because of the design of the clutch there is not a lot of room for the clutch plates to release, so when you pull the lever in you are really pulling hard against the end of the hub. I adjusted it to where it works, but leaves about 1/2-inch of free play at the lever and the clutch releases/engages in a space of about 1/8-inch. The design of the clutch seems backwards from what would be regarded today as normal. Obviously Yamaha didn’t continue with that design for a reason. Do you have any suggestions?
Secondly, after running the bike for a few miles and the bike is warmed up, the bike runs the carbs dry and you see a stream of bubbles coming up the fuel line from the carb to the tank. We checked for vapor lock in the tank, cleaned the carbs three times now, and installed all new jets and needle valves. The floats appear to be fine and are set at the recommended height. Do you have any idea what is wrong?
Someone suggested that this bike was known to have a problem with the carbs heating up and boiling of the fuel due to the high pipes, which form a hot box around the carb area. Not quite sure if that’s what it could be, but that doesn’t sound all that plausible to me. I could be wrong. — Ian and Craig Easton/via email
A: I haven’t had the experience of working on one of those models, but from the photos you supplied I can see that even in the best situation, you don’t have much leverage to pull the clutch release. I’d start by making it as slack as possible at the handlebar, then going back to the gross adjustment screw at the clutch release. Most of the manuals call for too much clearance here, often half a turn or more. I’d try to get the rotary pulled as far clockwise as possible, then adjust the gross adjustment to take up all the slack in the clutch rod, then back off 1/8th a turn. All you really want there is to ensure there’s no constant load on the clutch rod when the clutch is transferring power from the engine to the transmission. A new spring to pull the clutch release fully clockwise might help, too, if the one you have is stretched. Other than that, I don’t know what you could do that doesn’t involve re-engineering the clutch release to give more leverage. I certainly can see why they switched to the later version of the clutch release. One last thought: In your photos, the red paint visible on the clutch components may indicate that it was a balanced assembly. If you line up all the paint marks it may be that all the components form a balanced whole.
Regarding your fuel problem, you could try wrapping either the pipes near the carbs, or the carbs themselves with some insulation to see if that improves things. If it does, you know you have a vapor lock problem. Wrapping the header pipes near the carbs with pipe wrap may be the solution.