07 WR 290 miss difficult to cure

I recently installed an Athena 290 kit on my 07 WR 250.

Jetting is 40 pilot, OBEKR needle 5th groove from top, 172 main, 40 leak. Basically sea level to 100 ft, 50 degrees in NJ. Air box is opened up with a full GYTR exhaust system. Stock cams. ACV valve not bypassed, AIS is removed. Adjusted valves with new cam chain.

The bike idles and accelerates great, with a couple short backfires on decel. Just between 1/8 and 1/4 throttle, it will cough slightly or hesitate, then run smooth all the way to full throttle. It gets better when hot. I can ride around it, but it would be nice to make it go away. I've tried a 42 and 38 pilot with no change, and tried an OBEKQ needle, which would only run in the bottom groove (full rich). Any ideas? OBEKP?? JD?

Sorry guys, senior moment. I'm running the OBEKQ needle in the 5th groove from top. The OBEKR wouldn't work except in the bottom groove and then not well.

unplug the tps and test ride.


Warmed it up good and then disconnected TPS - no change. I noticed if you hold the throttle in the bad zone, then decel it backfires quite a bit. If you accelerate past it, let it wind up then decel you get no pops or just a couple short ones.

you were riding it for this test correct?

the ekr needle needs to be more like clip 2.


All tests are riding a thoroughly warmed up bike. The R needle I have is an OBEPR, not KR. The Q needle I have is OBELQ, not KQ. I apologize, my eyes aren't so good. Please let me know if that matters. The R needle in the second groove from top is infinitely worse, bike will hardly accept throttle. The only groove workable with the R needle is the bottom groove. The Q needle works pretty darn good in the 5th groove. This is regardless of 38, 40or 42 pilot jet. Fuel screw is 2 turns out. Any other ideas? I'm not too savvy on needles, what about a P?

EPR? are you sure?i know they are super hard to read.

when you say bottom you mean clip 7 from the flat end?


Yes, definitely EPR. Yes, 7th groove from flat end.


My EPR needle is Yamaha part 5NL-14916-PR. It's an optional needle for a 2007 YZ 250F. I bought it thinking it would help.

the issue is while hodling steady throttle?

Yes, right after 1/8 throttle, I'd call it 1/8+ throttle, if you hold throttle steady, bike will cough and not fire steady. You can keep it there doing that if you want. It will do it in any gear that can hold that throttle position for any length of time. Then, if you decel, it will backfire pretty good. Idle is fine, never stalls. It's easy to throttle right past it and go, but in tight woods enduro work it comes back to haunt you. I run A-super senior class. With the Q needle five grooves from flat end it's rideable but I sure wish I could eliminate it. Everywhere else in rev range bike behaves perfectly. Before 290 kit, when a 250, it was flawless. Bike was set up identical except main jet was 180, pilot 42, Q needle middle clip position.

Air filter is new (Uni) - I still have spark arrestor screen in airbox if that matters. Running Sunoco 93 Octane. That's the highest octane pump gas available in NJ.

tried leaner clip postions with the ELQ? clip 3 or 2?

you set the pilot circuit up via idle reaction to the fuel screw.

Yes, tried all clip positions with the Q needle. Best is 5th from flat end. But when setting up pilot using your instructions, I must say the bike was not overly sensitive to which pilot jet I used. The #42 pilot you could close the fuel screw and will still idle. The #40 reacts closest to your instructions, but it is 1/2 turn or less on fuel screw before it slows the idle. The #38 is more sensitive, slows the idle 1 turn out, stalls the engine at 1/4 turn. 3 turns out on fuel screw with #38 pilot races the idle up. So, I went with #40. Ran all last year (when a 250) with the #42.

But, 2 turns out on fuel screw, all three pilots actually work ok, no effect on the hesitation where I'm experiencing it. 50 degree day. I've tried all three pilots every needle setting. I can change that needle out in seconds now!

the pilto circuit will have no effect over anything that occurs with the throttle open.

when you say its best a 5th clip from the flat end,what are you basing that on?

did you have the slide out of the carb at any point?

The hesitation is minimized the most when clip is in 5th groove. 4th and 6th grooves from flat end make the hesitation more noticeable, easier to find with the throttle.

I honestly can't remember if I've ever removed the slide. I've heard it's easy to put in backwards. I don't think I have, but how do I verify?

hesistation? or steady throttle misifire? 2 different things.

the needle is tuned for steady throttle running.

anything that happens when the throttle is opened abruptly.

seems to you are trying to compensate for the ap circuit with the needle.

go to a 40 leak jet and do the o-ring mod.then go back and tune the needle for best steady throttle running.

its way rich on the needle.

I'm getting in trouble with my own words. AP is fine. Bike has no bog whatsoever, whack the throttle, front end comes up every time. Using 40 leak jet with Boyeson cover. The issue is only at 1/8+ throttle. If you hold throttle there, bike will continue to cough slightly.

I'm pulling the carb off and checking everything. I know somethings funny because you feel the Q is too rich.

I finished an enduro last Sunday and noticed much higher fuel consumption. Maybe because it's now a 290, but also like you say, too rich.

Q is not too rich.thats the straight diameter of the needle that isnt affected by clip position.but you say you have the needles full rich clip????? the high fuel consumption is becuase you are running the clip position too rich.

i personally would go to a EMP needle,3rd clip.

The Q I'm running in the 5th groove with ok results. The R needle ran best in

7th groove. Eddie, thanks for all your patience, I'm going to get a EMP and report back.


Ordered the EMP needle, put the clip in the 3rd groove. Much, much better. Thanks for the advice.

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