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roberts189

New Shims, more power, strange noise??

10 posts in this topic

I've recently changed my shims to gain the desired valve clearence and developed a starting problem where my 426 would only fire for a split second. I think this was due to over fueling so have adjusted the mixture to lean it up today but even with the adjusted mixture I get a crackling, popping noise when im not on the throttle.

My friend seems to think this is normal but my bike never used to sound this way and the revs seem to stick for a couple of seconds after releasing the throttle. Are these symptoms of it still being too rich?

please help

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Sounds like either there is gunk in the pilot jet or the fuel screw is too far closed.

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I've recently changed my shims to gain the desired valve clearence and developed a starting problem where my 426 would only fire for a split second. I think this was due to over fueling so have adjusted the mixture to lean it up today but even with the adjusted mixture I get a crackling, popping noise when im not on the throttle.

My friend seems to think this is normal but my bike never used to sound this way and the revs seem to stick for a couple of seconds after releasing the throttle. Are these symptoms of it still being too rich?

please help

Usually 'over-run' is a sign of being too lean. Especially at closed throttle.

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I've checked the timing and im sure its right, I havn't even turned the exhaust cam to YZF timing. My exhaust header is glowing quite bright too.

Without sounding too stupid could someone please tell me where the mixture screw is on my carb?

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interested in this to my bike has started to pop a bit when runing down hill with the throutle off.

never used to do it and ive not done any work to the engine.

what would happen if the bike was run to lean for to long? im guessing it would sieze up right?

it starts first kick hot or cold and the headers not glowing so is there anything worth worring about?

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usually when the header glows it means that there is extra fuel in the exhaust that is burning cause the bike is too rich. If it back fires and pops when you let off the throttle it is too lean.

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Without sounding too stupid could someone please tell me where the mixture screw is on my carb?

http://www.thumpertalk.com/forum/showthread.php?t=696672
interested in this to my bike has started to pop a bit when runing down hill with the throutle off.

never used to do it and ive not done any work to the engine.

what would happen if the bike was run to lean for to long? im guessing it would sieze up right?

it starts first kick hot or cold and the headers not glowing so is there anything worth worring about?

Some decel backfire is fairly normal in a correctly tuned YZF, and to a lesser degree, WR's as well. If it seems excessive, check for an air leak in the exhaust system. If you find none, work with your idle mixture.

Four-strokes are enormously tolerant of incorrect mixture in either direction, and will run poorly long before they are in danger from being lean.

usually when the header glows it means that there is extra fuel in the exhaust that is burning cause the bike is too rich. If it back fires and pops when you let off the throttle it is too lean.
Glowing headers are normal, particularly when running YZ timing, and are a product of retarded ignition timing at idle, and aggressive cam timing. A YZ header will reach 850 ℉ in less than two minutes at idle quite easily.

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I did notice the other day when I forgot to take the bung out wen kicking it there is a slight leek in the joint. So im guessing that its running rich and the popping is caused by the exhaust leak?

il try sealing the exhaust and leaning it up abit and il let u know how I get on.

Thanks for the help

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Try just resealing the pipe first. Adjust the pilot to make the engine run right, not to deal with popping.

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