'03 yz250f..Stumbling through midrange

[Pothole]

I've read the FAQ's probably 10 times over the years and this one has me a little confused. '03 yz250f w/ powernow, 262 kit, drd pipe, and vortex ignition...runs great off idle (no bog whatsoever when wicked open fast) and through 1/4, stumbles through the midrange, then rips clean and crisp from 3/4 to WOT. Any ideas?

[Wayward Son]

stumbles while accelerating wot?

sounds like rich main jet to me.

[Pothole]

stumbles while accelerating wot?

sounds like rich main jet to me.

Not exactly...it will come off idle cleanly, stumble and kinda hesitate through the midrange, then once the revs build it runs clean and crisp all the way up. It's just that 1/4-3/4 range that it hesitates.

[Wayward Son]

but has the throttle been fully opened at that point?

[Pothole]

but has the throttle been fully opened at that point?

nope, the problem is just after 1/4 and before the throttle is wide open. once the throttle is wide open, the bike runs very clean.

[Wayward Son]

as long as this inst happening as your opening the throttle fully i would say your rich on the needle.

[Pothole]

as long as this inst happening as your opening the throttle fully i would say your rich on the needle.

Thanks Burned, I'll drop the needle a notch and report back.

I guess I could have described the problem in another way...when holding the throttle at a constant 1/2 throttle postion, the bike feels like it's loading up, or kind of stumbling or hesitating.

[Wayward Son]

ok,steady throttle is definately the needle.

[trailrider121]

Thanks Burned, I'll drop the needle a notch and report back.

I guess I could have described the problem in another way...when holding the throttle at a constant 1/2 throttle postion, the bike feels like it's loading up, or kind of stumbling or hesitating.

Pothole,not to intrude on your question.But I'm fighting the same question.

Burned,

I have the same problem but its around a constant 3/8 throttle.Same symptoms as above.My bike is a 03 RM250 with a JD kit.I have called and emailed JD,and he called back with some options and its better but same problem is still their,very hard to get answers JD must be busy.I'm running the Blue needle @2nd clip.Is the needle to lean or rich?

[Wayward Son]

try the red needle 3rd clip.

[trailrider121]

I'll try the red needle again.Well Burned, maybe I should give you my current specs you might see something wrong in my setup.I tried the red needle at 4000' when i first got the kit.The bike ran good from 0-1/4 and at 3/4 -Full throttle,anywhere between it would stumble almost like someone was pushing the kill button very fast.Very strange.I ride mostly around sea level to 3500'.I feel I'm very close to the jetting.

My current combo:

162 main

42 pilot jet

A.S. @ 1 1/2 out

45 power jet

7.0 Slide

Race gace mixed @32:1.Only mods I have are a Bills Pipe and RadValve.

[James_Dean]

Anthony,

As I mentioned in the email 10/2-

"Use a smaller main jet (#160) and clip position #2 from top."

I was referring to the red marked needle, not blue. Did the bike run too lean or have you tried red #2 yet?

--I'm not too busy to answer your emails, nor have I received any emails from you since.

Thanks,

James

[trailrider121]

Thanks James,

I have not tried the red needle at #2 from top.I will try out the red needle tonight.I will post my results.I want to get this figured out before my race in two weeks.Thank you for your time James.

[Ingo]

Sounds like my problem. I dropped the needle one clip and voila! Sorted. See my post on the WR290F @ 4600ft.