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

 

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

A: The oil won’t be ideal, but it won’t be as bad as the gas would be after all those years. I’d drain the oil reservoir and put in fresh synthetic 2-stroke oil. If you have access to the oil pump, most of the time there is a small screw backed with a fiber washer on the pump body that is used to prime the system when completely drained. You could remove that screw and let fresh oil flow down from the tank through the pump and then seal it up again. Modern 2-stoke oils are a vast improvement over the old formulations. Spectro Performance Motorcycle Oils makes several kinds of 2-stroke oil. Check out spectro-oils.com

Suzuki misfire

Q: Hi, Keith, I’ve acquired a 1982 Suzuki GS1100EZ that had sat for many years. All fuel and brake systems have been completely overhauled. The engine starts, idles and runs perfectly until 7,500rpm, 1,500 short of redline. At that point regardless of load or road speed there is misfiring and no rpm increase. The intake and exhaust systems are stock as is the carb jetting (110 mains). I have ohmed out the coils and wires as well as the pickups and all are within spec. After many years of tuning and repair I find myself stumped as to whether I have an ignition or fuel problems. The spark plugs show a white color indicating a lean condition but everything is stock. Any help would be greatly appreciated.

Joe Padula/via email

A: Thanks for the detailed background of steps you’ve already taken, that’s very helpful. The early ’80s bikes almost universally suffered from fueling issues due to attempts to meet California emissions standards. Since you’ve done all the leg work scoping out the ignition system I think your next step should be to buy a set of main jets one major size larger and see if that improves the wide open running. As a quick check to see if this might help, if you can do it safely, try using the enriching circuit at wide open throttle. If the bike suddenly surges ahead, you’ll know what to do.

More carb issues

Q: I have a 1979 Suzuki GS550L with low mileage that we rescued from a backyard in Amarillo, Texas, a couple of years ago. After a bunch of elbow grease, updates, new parts, etc., the bike has been returned to life. We upgraded to electronic ignition. My problem is that the bike runs great up to about 4,000rpm. It starts easily, idles evenly and has excellent power until about 1/2 throttle. The thing acts as if it had a governor. It just sort of stalls out and will not accelerate. It reminds me of a rev limiter at a shift point. The bike is timed correctly and the centrifugal advance mechanism is working correctly. At idle, about 1,000rpm the timing is at the “F” mark and will fully advance at about 2,500rpm. So I don’t think timing is the issue. The bike has a set of rebuilt carbs. It just seems like the main jets are allowing fuel to flow at the upper rpm’s. I need some help. The bike runs and rides great in the world of idle to around 4,000rpm, but will not accelerate beyond that. Help!

Mike Baker/via email

A: My answer here is about the same as above, a quick test would be to apply the enrichment circuit and see if that improves things. If so, try larger main jets.


Email questions to keithsgarage@motorcycleclassics.com

Published on Jun 12, 2020

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