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 have a 1981 Honda GL500 with 61,225 miles. The bike starts and runs up to about 4,500rpm, then breaks up and runs really rough. In terms of problem solving, I’ve done all of the typical tune-up items including replacing the air and fuel filters, and the spark plugs. I have also cleaned the carburetors. None of this solved the problem. After research on a CX500/GL500 forum, a member suggested replacing the spark plug wires and the coils, which I changed. This didn’t solve my problem either. I then located your article on CDI units and their function, and it seemed like the logical solution since I’m losing high-end. After changing both to a set ostensibly from a low-mileage bike, it still didn’t solve the problem. Do you have any suggestions? — Phil Quattrone/via email
A: Running problems with the CX/GL 500/650 bikes can be difficult to pinpoint, as there are several troublesome systems that can cause your symptoms. One of the toughest problems to solve is carburetion. The CX/GL Keihin carbs can be difficult to clean completely. See our article in the March/April issue about the CX500. The owner of that bike has written a comprehensive book on thoroughly cleaning and disassembling CX/GL Keihin carburetors. MC