2007 yz250f
at Denver and Colorado Springs MX track
6000-6500 ft, 60-70deg F, 20-30% humidity (sometimes at 8500+ ft)
Stock with pro-moto billet spark arrestor, twin air filter, ez ajust fuel screw.
Valves were just checked
No exhaust leaks
Hot start properly adjusted
All adjustments confirmed on track, not on the stand
jetting (xxx) = stock
172 main (178)
48 pilot (42)
(OBEP-Q) needle 4th down (5th down)
fuel screw 1-1/2
leak 70 (80)
The problem:
The bike feels like it could have better acceleration. I don't have a noticable bog, it just seems to slowly climb to redline. But feels strong at full rpm and plug looks good. Exhaust tip is black lightly sooted.
I first raised the needle clip from 5th to 4th (leaner) and it felt better but it developed a rarely occuring hicup when accelerating at about 1/2 to 3/4 rolled on throttle. I decided to leave it at 4th and proceed to the pilot jet.
i tried a 42, 45, and 48 pilot jet and did the fuel screw adjustment properly (per the sticky) every time:
42 at about 2-3/4 turns had best accel but popped on every decel very bad (too bad), when to as much as 3-1/2 out and it made no differance.
45 at about 2 turns out had better accel then the 48 but not as good as the 42. the popping was improved over the 42 on decel but still frequent but shorter duration. went out as far as 3-1/2 turn and it mad little differance.
48 at 1-1/2 turn out worst accel, best popping (almost none existant)
I would like to know without looking at my symtoms what a baseline jetting setup should be (why is my pilot going richer and the main leaner then stock?), and then how that baseline might change to address the symtoms.
Should I try the 2009 NHKR needle the posts are raving about and a 40 leak jet?
