QuestionHey Bill I asked a question almost a year ago about this bike. I have since had the carbs gone through and cleaned. It ran like a champ all summer and into the fall. The past couple weeks it was to nice to pass up a couple of mid winter rides. As I was taking my bike for a ride around town over the weekend, and towards the end of my ride I notice that the bike, when stopped, had a really hard time getting up and going. As I payed more attention it seemed that the bike would almost stall out or putt along till I hit about 15mph and then would come back to life and zoom right along. I don't hear any nasty noises coming from the engine so I don't think things are grinding around in there. Last time I talked to you you said I need to balancer shaft adjustment and check the camchain, would either of those be the issue, or would you have insight to the problem.
Thanks a ton.
Jared
AnswerJared, the camchain and balancer chain are basic maintenance items, but don't really affect performance unless you let the camchain get REALLY loose.
Off-idle and low speed acceleration issues are usually to do with the accelerator pump functions, as well as idle jets and primary main jets.
http://www.cmsnl.com/honda-cm400a-hondamatic-1981-usa_model7284/partslist/E++200...
Looks like you have an air-cut valve (anti-backfire valve) which can have a diaphragm failure, which causes an air leak that makes an erratic idle, plus some backfiring on deceleration. If the accelerator pump isn't getting the full squirt into the carb throats, the mixture will be too lean to help accelerate the engine. BTW, there are aftermarket kits to repair the accelerator pump diaphragm and the air cut diaphragms, which are much cheaper than OEM Honda parts, which may be out of stock now.
I would try to increase the primary main jet sizes from #68 to #70 to help out with the flat spot in the transition period from idle to part throttle.
Bill Silver
