Fire Thrower 07 450???

This is a new bike...and my first 4-stroke. I put a PMB endcap on because I'm going to need a S/A. The screen stays out until I need it though. My question is; when I put the cap on my bike, it seems to pop and crack more while revving it. I've been doing some night races and a flame shoots out the back pretty frequently. It does look pretty awesome, but I would much rather have my bike running I'm hoping that it's just the fuel screw, but any help would be appreciated.

07 yz450f.... Everything Stock so far

91 octane


It is running too lean. If it is popping when you are 1/2 throttle to wide open. then you need to richen your mauin jet. If it is popping at low RPMs and on deceleration then you need to richen your fuel screw or pilot jet (if your fuel screw is too far out then go bigger with your pilot and turn your fuels screw back in).

I know there must be a step by step guide on how and when to adjust your fuel screw and jetting on here somewhere. I looked the other day but couldn't find it.

Could someone post a link?

Edit: Forget that, I got off my fat arse and looked in the FAQ at the top of the YZ450 section. Heaps of useful info there!

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