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: My 1988 BMW R100RT has 43,000 miles and runs well most of the time. It loses power randomly and for various durations. So far I have changed the plugs, rebuilt the carburetors, cleaned the kill switch, cleaned the ignition switch, added contact paste to the heat sink next to the coils and synced the carburetors. Last time I had the bike running I kept hearing a random sparking noise when I was near the gas tank. I took the tank off and put the bike in a dark area to try to see where the spark was happening but I could not locate it. Based on what I have read, it appears that the coils might be the problem. I think it has the original coils on there now. Is there a simple test I could perform for the coils? Or if you feel that it is the coils please tell me where I could purchase them and which resistance spark plug wires I should buy. — Peter Economou/via email.
A: The random sparking noise may have been the coil wires grounding to the gas tank, so when you removed the tank you removed the spark path. If you replace the plug wires, use resistor core wire from an auto parts store with non-resistor plug caps. If you use wire core plug wires you’ll want resistor-type plug caps. Wire core wires and resistor caps are usually available at your local motorcycle shop. You may still end up replacing the coils but you may find your problem fixed by new wires. MC