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Triumph Bonneville T140V Hard to Start

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 am the original owner of a 1978 Triumph Bonneville T140V. For the first four years of its life, it was the focus of most of my attention and I put 44,000 miles on it. Then life came along and the bike sat in the garage for more than 20 years. In 2011 I was given some parts for Christmas and the journey back to life for it began. Since then I have had the engine completely rebuilt, the carburetors thoroughly cleaned and have done tons of other maintenance so now, even after sitting (battery on tender), it starts with usually less than three kicks from cold. My problem is it will not idle when cold, and when hot will idle at a high 1,500rpm, but will die off at an intersection if I do not blip it occasionally. I have the original carbs, but found one to have an oval slide barrel, which I had fixed. I also tried to use another set of carbs but still have the problem. Can you offer some advice?
— Karl Stram/via email

A: I always advise people to not tune their bikes so they idle well cold. They don’t stay cold long, and then they’re running rich when they reach operating temperature. As for your high idle when hot, a few things can cause this. An air leak leaning out the mixture is one. Another, fairly common issue is a sticking auto advance unit, assuming you are still running points. I’d start by gapping the points and making sure the timing is correct, and confirming that the auto advance is lubed and working. After that, I’d look for air leaks around the carburetors, which you can test by spraying around the carb mounts with water. If the idle changes, you have a leak. In an effort to stop people from distorting the carburetor by over-tightening the mounting bolts, Triumph had moved to cupped washers with O-rings (they called them insulators) under them. If those are missing or flat, there is a good chance for an air leak around the O-ring that seals the carburetor to the manifold.

Published on Oct 23, 2018

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