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jetting problems?

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say you have a carb on a 99 yz400f jetted almost perfect. how much air does it take to throw the mixture right off and lean it right out. reason im asking this is because my jetting was really good according to the plug and then almost out of no where it went lean. its been running lean for a real long time now and i think i might have found the problem but not sure its enough to change the jetting as much as it did. i was told i had an air leak, and when i was inspecting stuff today i noticed that on the hotstart theres a little rubber dust seal right behind the red knob. that seal was out of its groove and out about 1-2 mm causing the knob to be pushed out a very little bit. i took it off and blew through it and it turned out to be leaking a tiny bit of air. i haven't had a chance to test ride it yet with the seal back in place but would that tiny bit of air cause a engine to run as lean as it is. when i checked the plug before it was darkish brown in the middle and black around the ring, for tha lsat little while when i checked it, it was white in the middle and black around the ring.

thanks

shane

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That could very well be it, it doesn't take much. Look at the size of the holes in the jets. A hundredth of a millimeter on the needle diameter can be the difference between ecstasy and disappointment.

If fixing that air leak doesn't cure the problem, try squirting starting fluid around the intake boots, carb clamps and anywhere else there might be a leak while the engine is running. If it speeds up, you've found another.

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alright i try it out. i was told just squirting water around there would do the same thing, but i tried it and it did't work. starting fluid as in ether. i got some of that but thats pretty damn explosive.

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...pretty damn explosive.

Yup, take your cigarette break AFTER this test, not during. :cry:

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