Question about Triumph Bonneville Motorcycles

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I've got a 1972 Bonneville T120V with a problem. After 25-30 miles, it won't tick over but will start up straight away. I can rev it up, but it pops and bangs a little, can you help please. Thanks

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Oh, something is telling me to stay away from this one. It has been a long time since I messed with a vertical twin triumph.

The first thing to do is to check the points and timing. Check and reset the points first. Usually if no one has moved the plate, the timing comes right back into specs with the points gapped correctly. But, just to be on the safe side, check the timing once you get the points right.

Next is the carbs. Hopefully you aren't still running the original Amal carbs. The Bonneville had twin carbs and they need to be balanced pretty well. You need a carb syncronizing tool to do this with. It works off either manifold vacuum or air velocity through the venturi. You can play with the idle mixture screws and idle speed screws and maybe get it close. But, unless you are somewhat familiar with any of this advice, I'd look for someone with some experience to help you with the job. If you get the timing too far off or the carbs too lean, the Bonnevilles were terrible about burning pistons. We don't want that do we now. Good Luck, Steve

Posted on May 05, 2010

  • Ignacio Martinez V. Dec 17, 2010

    Steve is right however you must also check if there's an air lick going into the carbs or the exhaust system. Cold air usually causes this misfirings. Make sure these components are air tight



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I've got a 1972 Bonneville T120V with a problem. After 25-30 miles, it won't tick over but will start up straight away. I can rev it up, but it pops and bangs a little, can you help please. Thanks

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