AboutBill Silver Expertise Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.
Experience I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.
Organizations VJMC (Vintage Japanese Motorcycle Club) of North America
Publications VJMC newsletter, as editor for two years and as contributing editor currently.
Question Hi, Bill. I've got a newly acquired 1980 CM400-A, history and mileage
unknown. The bike revs fine on the centerstand in either gear as long as there is no resistance from the rear brake or from trying to ride down the road. However, under load the engine makes noise like gears slipping or a chain slipping off a sprocket tooth. Engine also jerks and stalls. This problem occurs ONLY under load, suggesting that there are worn gear components or some engine chain/sprocket slipping under those conditions. (1) I’m wondering if there’s anything that’s accessible behind the right engine cover that may be responsible---can a bad torque converter do this? I have a Clymer manual and experience with general bike repairs, but don't know anything about hondamatics. Any ideas what to look for? (2) Do you know if other year CM400-A or CM450-A motors can be installed in place of this one?
Thanks!
--garcia (garicao@hotmail.com)
Answer Garcia, Check the ignition system over and certainly the carburetors and fuel flow from tank to carbs. Any issues with poor running can set up a lot of instablity in the rest of the power train.
CDI systems in the early automatics were all known to have problems. Try to get a timing light on it to see if the spark advance is functioning properly. Maybe the spark module is causing you grief. Be sure that the plug caps are in good shape.. 5k ohms and the plugs are fresh.
There could be a mechanical problem in there, too. I don't have any real info to share about troubleshooting the automatic, but do know that you need to check the balance chain adjustment under the right side cover where the converter is. Drain the oil and see if there is metal debris in it. That would indicate mechanical failure. If oil is clean, reset the balancer shaft chain tension, give it a good tuneup and try it again. The camchain needs adjusting periodically, as well.
I think that other A motors will fit that chassis.
