3 replies to this topic
  • charger1hazzard

Posted May 09, 2011 - 06:48 AM


all stock, i live in centrel ny. it is jetted for a pipe that did not come with my bike. so i have to jet for the stock pipe. my local dealer said the stockpilot is a #42 but is it a 21 series or 22?

Also he bike doesnt feel insanly fast? i had a few yz250s before.
And my plug is sarting to foul. so would this be why it doesnt like to start hot and stalls at low rpms. not like puttering low but just doesnt like to go slow if you do it will stall easy.

and if you put in to much oil will it make diff. noises? i got to change it again but i had a hole in clutch cover so i added about a qt of oil to be safe after i fixed it

  • grayracer513

Posted May 09, 2011 - 07:58 AM


You haven't specified your year model, so I can't tell you what your stock pilot was.

All YZ450's up through '09 use an FCR-MX carb, which uses series 21 pilots. The part numbers for stock and alternate sizes and your original stock jetting is listed in the manual.

Hot starting a YZF can be trying for the uninitiated, especially coming off a two stroke. The thumper has an accelerator pump, and what you must not do is the whole thing of twisting the throttle as you crank that so many two-stroke guys do. You'll pump the engine so full of gas that it won't start for a week. Zero throttle, hot start lever pulled, and crank.

The YZF was built as a full-on MX race bike, not an enduro or trail bike, and they don't do low speeds really gracefully. The engine is high strung and has almost no flywheel weight to help it stay running. Too fat a pilot jet makes this worse, but again, you haven't told us what year your bike is, what size your pilot jet is, or at what altitude you do most of your riding.

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  • charger1hazzard

Posted May 09, 2011 - 08:20 AM


1500 ft aboe sea level. 2005 all stock except jetting. dont know my jets havent took carb apart yet

  • grayracer513

Posted May 09, 2011 - 08:26 AM


Read this:


...and download a manual:


The fact that you have an all stock bike doesn't mean your jetting will be correct with a stock pilot, but a lot of people use one way too large for a lot of the wrong reasons. Start by finding out what yours is and trying an adjustment based on the first link I sent you.

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