Electrical, 2-Strokes, Misfire and Carb Issues Q and A with Keith


 Motorcycle Classics tech expert Keith Fellenstein
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, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an email with “Keith’s Garage” as the subject.

1978 Triumph T140 Electrical issues

Q: I have a 1978 Triumph T140 with stock points ignition that has lost spark. I ran the bike a couple of summers ago with an old, possibly highly sulfated, battery. Since it’s a kickstart bike I didn’t need the battery for starting. Anyway, I started the bike and began a short ride. About 5 miles out, I lost spark and ended up trailering the bike home. I parked the bike, rode others, and haven’t done any troubleshooting since that incident but would like to get the bike going again this spring. I guess my question is can major damage be done, like stator damage, etc., by operating with an old discharged battery? Thank you for any assistance you can provide.

Mark/via email

A: It’s possible but unlikely to damage the generating side of the electrical system by running with a damaged storage side. If the battery has an internal short the alternator will run at full output all the time. In this specific case though, it’s unlikely. The Lucas charging circuit in your Triumph runs full tilt all the time anyway, and depends on the Zener diode to dump excess current to ground when the battery is charged. Here are a few ways to troubleshoot your electrical system. The first would be to test the alternator windings for continuity and short circuits. Disconnect the green/brown and green/yellow leads at the rectifier and use a voltmeter (if you don’t have one, get one, they’re essential) set to ohms or continuity. Place a lead on each of those wires and the result should be close to zero or a beep if set to continuity. Put one lead on a wire and ground the other one, the results should be 1 on a digital meter and no beep if set to continuity. If all this checks out all you’ll need is a new battery.

Reviving 2-strokes

Q: I did not like 2-stroke bikes when I started riding motorcycles in 1967, but after they went extinct I bought a couple of Yamaha RDs and a CT 175. My question is, at the time I bought them they started and ran OK, but after sitting for 12-15 years, I know I need to clean out the carbs. I couldn’t drain the carbs because they sit right on top the crankcases and there is zero clearance between them. But what about the auto lube system? Do I need to do anything to make sure they still work, like flushing the system and replacing the oil? I haven’t found a source for proper 2-stroke oil for motorcycles. Thanks for your help.

Bing Fong/via email

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