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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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Old 4 Dec 2003
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crackle and pop

The old XT is playing up again, there seems to be a carbouration problem. It seems as if the carb is moving in time to the engine (back and forth) and thus the manifold is loose. It runs OK at high revs but when left to tick over it seems to every 30 seconds or so explode or pop.
it sounds as if air is being pushed back to the carb, its only on the right side (secondary carb). could an air leak from the loose manifold do this?

Ive tried tightening but it seems to be knackered however I don't want to replace it if it's not the problem. again other than that it goes fine but may get hot if I leave the choke out at lights (to keep it ticking over at 2500 rpm)

any thoughts appreciated
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Old 4 Dec 2003
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If the rubber inlet manifold is "pulsing" in tune with engine revs, then there's nothing to worry about. On the inlet stroke, the engine is sucking in a lot of air, especially on a single. Lots of bikes do it to a lesser or greater extent, nothing more than the walls of the inlet manifold flexing.

If the manifold is tight to the head & the carbs are tight in the manifolds,then you may be running slightly lean. Try adjusting the mixture screw on the underside of the carb. Screwing it out in 1/8 turn increments will richen the mixture.

If problem still persists, check the air filter & exhaust fitment or alternatively, buy my R80GS....

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Old 4 Dec 2003
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Seems like lean mixture, and the fact that it suddenly appeared leads to the diagnosis that the inlet rubber has come loose from the piece of metal that it is vulcanised to. And this piece of metal is bolted to the head. So, there is a gap between rubber and metal, the rubber moves slightly with the pulsating pressure in the inlet and the gap lets in air that has not passed the carb.
A test I have heard of: spray a little engine starter stuff around the rubber. If, at idle speed, the engine speed increases, the inlet rubber is defect. No tinkering, buy a new one.
This is a common prob with the XT6.

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Old 4 Dec 2003
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Last year, I discovered a hell of a lot of carbon in my carb.
On investigation I discovered that the previous owner had lengthened the cam-chain tensioner by welding a bolt onto the end of it.
This resulted in a stretched cam-chain, over advancing the timing and causing exhaust gases to blow up into the carb.
May be worth checking your timing, perhaps it's just slightly out?

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Old 5 Dec 2003
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Geoff - I know I shouldn't laugh, but I had to. The previous owner obviously wasn't one to be constrained by conventional thinking!Regards
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Old 5 Dec 2003
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Thanks for the replies, on inspection it seemed the manifold was OK but was still moving which points to the un vulcanised rubber from metal. Ive orderes another manifold and will adjust the mixture if it continues.
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