Accelerator pump adjustment for 2003 WR450


I've been fighting a variable idling problem with my bike and think that it's just getting too much gas from the accelerator pump. I researched the BK mod but it doesn't seem to need it or even work on the 2003. When I read the (Canadian) manual on adjusting it, the instructions seem backwards.

The threads on adjusting it discuss timing and duration, but the adjustment seems to only deal with duration as it is always pushing on the pump lever.

So, I just went riding with a screw driver and found that the bike runs best (no hesitation) with the screw all the way out. As in, I took the screw out and put it my pocket. Stock it was 3 turns in. I'm at 9,100 feet, 96 db modified pipe, 155 main, 40 PJ, 2003 stock YZ needle/4th position and 2 3/4 turns on air screw. My jetting is almost perfect. Any leaner and I lose power.

The idle problem is not cured but is better. Anyone have this same problem?

My next step is octane booster as this made my 2001 and 2002 run better. :)


Are you compensating for a lean pilot circuit?

I started the PJ stock at (stock) 48 and slowly went down to 38. 40 is the best and is the only one that lets the bike start with "the button". I've also gone from 3/4 turn to 3 1/4 turns on the air screw. 3 turns was stock and I'm at 2 3/4.

My ac pump is in 1/4 turn from the factory position. I have not tried all the way out but my understanding is a shorter duration is more desirable. Maybe Taffy can help here.

There was an article in Motocross Action for the YZ450, they said to turn it in 1/2 turn. So thats what I did on my WR

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