Triumph T100 Plug Fouling

A reader’s Triumph T100 keeps fouling its plugs and he assumes it’s oil. Does Keith have a different perspective?

Reader Contribution by Ed Gottshall
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by 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.

Q: I have a 1965 Triumph T100 500cc. I’ve restored it externally to look like my 1964 but have not cracked the engine. My problem now is the plugs are fouling. My solution so I can ride is to carry clean plugs and change them when fouling occurs. I’ve run a compression test and the readings are a little below the minimum value. My local mechanic, who is quite good with Triumphs said he has seen them run with levels lower than mine and not have problems. The plugs are wet black and I assumed oil. Maybe I’m wrong and it’s gas which would be carburetor. May I have your thoughts on this? I’m trying to sell the bike and I’d like to fix the problem. Both plugs foul at the same rate. Thanks!

– Ed Gottshall/via email

A: Ed, you didn’t mention how many miles were on the engine, but a common problem with these engines is worn valve guides. With that you would have fairly normal compression, but constant oil leaking down into the cylinders. If you want to investigate further, pull the intake manifold and exhaust pipes and look for fresh oil on the back of the valves. If those seem normal, then I’d try dropping the carburetor needles one notch and with new plugs; see if that changes the plug colors. MC

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