Why is my en­gine pop­ping and bang­ing?

Motorcycle News (UK) - - GARAGE -

Af­ter 35,000 prob­lem-free miles my Yamaha TDM900 has started to pop and bang on the over­run. The are no ob­vi­ous air­leaks and the ex­haust valve clear­ances are all within lim­its. Alex Aber­crom­bie, South­sea

A

An­swered by Stu­art Gaines, Yamaha tech­ni­cian As you say the clear­ances are OK, the cul­prit could be a de­vice called the ‘coast­ing en­richer.’ These bikes nor­mally run very lean and if you shut the throt­tle off rapidly the twin­cylin­der can cut out, so there’s a little spring-loaded valve that cuts the air off to keep it rich enough. It’s mounted on the left side of the left-hand carb un­der a screwed-on al­loy cover. Pull it out and give it a good clean.

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