Triumph T120 Tiger Spark Troubles


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 e-mail with “Keith’s Garage” as the subject.

Q: I have restored my 1971 Triumph TR6R T120 Tiger from top to bottom. The engine and electrics were professionally done, while I stuck to the other things. I’ve had the bike out half a dozen times and all seemed fine. Recently, while riding my Tiger, which now has 168 miles on it after the rebuild, my engine decided to run on one cylinder. I limped home. The coils are original Lucas 17M12. I checked for spark at the plugs first, the wires secondly, and got spark on the left side (as I sit on the bike) but not the right side. The bike has a new Pazon ignition in it. I then switched the wires to the opposite, and also did the same with the plugs and the coils. I got the same results on the right side — no spark. I took an ohm reading on both of the coils and got 4.7 on the primary side, and 5.36 and 5.3 on the secondary sides. I also changed gas. Upon start-up after all of this, the bike ran fine for about 30 seconds and then the right cylinder stopped running again. Am I on the right track to assume that I need to replace the coils? Both sparks are orange/light yellow when they fire. Are the coil ohm readings correct/within specifications, or does it indicate that they need to be replaced? The book says 3 ohms minimum and 3-4 ohms maximum for primary resistance, but nothing about the secondary resistance. Maybe I’ve answered my own question, but I’d like to hear from an expert if I am on the right track. — Burt Horner/via email

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A: The biggest problem I can see is you are running two 12-volt coils in series in a wasted spark ignition system that calls for two 6-volt coils in series. Since the Pazon charges and fires both coils every time, you are giving it too much of a load to deal with. Switch to two 6-volt coils in series or get one dual output coil of 3 ohm primary resistance and I think your problems will disappear. Update: I got an email back from Burt, and after changing to 6-volt coils and chasing down a grounding problem, he’s on the road again.

1/13/2018 12:33:58 AM

I'm glad he got that sorted. Two 6V coils are always recommended. Beware of dual-lead coils with the OIF models. Mounted under the seat they need a heat sink. I had one Harley coil go low resistance on me. I can only assume that it got hot. Fried my Boyer. It helps to put a 5A fuse in the power lead to the black box just in case.

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