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08 Yamaha YFZ 450 Jetting Issues HElp!

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I have an 08 YFZ450 with hotcams and an aftermarket exhaust. I just moved to Colorado where the elevation is 6000 Ft. Much higher than Illinois. I had a guy jet my quad while i was in illinois with the dynojet jet kit and he put in the 126 main jet and the dynojet pilot needle with the e-clip on groove #3 from the top. I just dug into it to see what i needed to do for the jetting and the jet that he put in is the one dynojet suggests for elevation above 6000 ft. (the 126 main jet) I have the fual mixture screw turned out one turn. My bike idles pretty smooth but it backfires when i crank the throttle to about half. Any suggestions.

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since stock is 150 you should not jet down with a an aftermarket exhaust instead you should use anything above 150 and yes your bike isn't working because 126 is too small

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I put in the 165 main jet and i have the mixture screw turned out 2 1/2 times. and its still doing pretty much the same thing. It idles fine but when i hit the gas really fast it either sputters or it dies. Should i get a new pilot jet. Right now it has a 42 in it. I called a local shop and he said to use the 42 and leave the main jet at stock whitch is 140. I'm pretty lost and not sure which way to turn.

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From what I understand the dyno jet needle and standard kehin jets are not compatible so you will never be able to get it jetted right. Here in Colorado I have jetted many different ATV and bikes almost all of them run the same jetting a 170 main needle on the third clip and a 48 pilot and fuel screw 2-2.5 turns out all kehin jets and needle you will want to run without the lid on the box with this set up. You also need to check to make sure the accelerator pump is not hitting to soon. What part of Colorado are you in

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