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Temperature sensitivity

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My 06' WR250F was born in Virginia but now lives in Minnesota.

This past weekend I was riding with temps in low 50's. I noticed a flat spot just off idle. To correct it I incrementally turned the zip-ty fuel screw from its normal 2 1/4 turns to 3 1/2. My pilot jet is #42. This corrected the flat spot, but I have seen advice that if you go above 3 turns one should go up a size in pilot jet (#45).

My question to those who ride in colder weather is should I go to the #45 pilot jet or just rely on the fuel screw even though I'm pushing a boundary?

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Cold dry air will like being a little richer. Down here in Texas I will change the main up one size in the winter and tweak the fuel screw. However that is just for a couple of months. The rest of the year it is on it's normal jetting.

Sounds like you can get away with a larger pilot year round though since you were at 2 1/4 before. Give it a try, you can always swap back. Just document what you've done so you know what to do next year.

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IMO, a 45PJ for 50F is too rich for your bike.

I have found that my PJ and FS jetting for 80F compared to 50F (for example), can be corrected with a 1/4 turn of the FS. MJ should be raised one size.

I have a question- How long has this bike been sittting? If the bike was sitting for a while (like a couple weeks or longer), it is quite possible that your current pilot jet is gummed up. In this case, pull the pilot and clean it out.

Also, old fuel can sometimes cause jetting issues too. And/or, another thing- In Minnesota, our premium pump gas typically has 10% ethanol which will result in lean jetting (approx one size lean). Find some of the non-oxygenated 100% premium and try that instead.

Good luck with it.

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All, thanks for the replies.

Bazooka you make an interesting point. Does the fact that I needed to go more than 1/4 turn on the FS indicate its masking a problem that one larger MJ would better address? The flat spot was just off-idle and perhaps the MJ is having an effect. BTW, the bike was stored for the winter without any fuel in the tank or float bowl.

I'll give both ideas a try. First a larger PJ then try a larger MJ. Jetting is kind of fun when you only make one change, test it out and document, document, document.

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The reason you can't go more than 3 turns on the fuel screw, BTW, is because any further than that makes it likely to fall out. Probably don't want that. :)

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Dverbeck,

Often times, draining the fuel causes more trouble than if you used Stabil and left fuel in the carb. The residual fuel is enough to gum up the jet passages. I'd take a close look at that #42 for partial plugging.

You might also try raising the needle one clip. Keep in mind that if your bike still has the stock jetting, your needle will only have one clip and you'll need to either get a washer under the clip or just get a different needle. I have found pretty good results with the 08 YZ250F needle in my 05 WR250F.

Another thing to verify, is leak jet number. Are you getting the dead spot from opening the throttle quickly, or is it a dead spot with a slow throttle roll on?

Btw, here's some time saving carb working pointers for you:

-->> Removing and replacing needles.... There is an easier way to R&R the needle than the manual describes. a) Remove hotstart connector from carb body. :) On a WR, unbolt the regulator. c) Rotate carb to the right side. d) Have at the needle. e) Note that using the needle grabber tool from either the newer YZF or CRF makes it much easier to get the needle out of the slide.

-->> R&R the leak jet.... a) Loosen carb boots on engine and air box sides. :banghead: Pull carb loose from boots. c) swing carb out towards the left side of the bike. d) Have at the bottom of the carb to remove the float bowl.

-->> R&R main and pilot jets.... Both are accessible from the bottom of the carb w/o rotating or removing the carb. It is a good idea to lay a rag on the engine to prevent the jets from dropping into the frame. The MJ is very straight forward and no need to explain. The pilot can be R&R'd with the proper length screwdriver. To replace the PJ, I made a tool from a small nail (#4 or #6 common?) Grind the end to be lop-sided & pointed end so you can stick the jet on the end of it. Use this nail-tool to guide the PJ up into the carb and give it a rotation or two. Use the screwdriver to finish the job.

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Bazooka,

Raising the needle (lowering the clip) is another good idea. I really appreciate the R&R tips. Rotating the carb is now much easier since I removed the AIS.

Trying to alleviate: Off idle roll-on flat spot. Not the dreaded wacka-throttle bog.

This is my current set-up:

MJ: 180

PJ: 42

LJ: 60, thin o-ring mod

FS: 3.5 turns.

Jet Needle: JD Red clip 3

Airbox: snorkel removed

Exhaust: Stock with insert removed

Plan - try the following independently:

1. Check for fouled PJ. If so FS back to 2 1/4.

2. FS back to 2 1/4 or less, raise needle.

3. FS back to 2 1/4 or less, PJ #45

Any other suggestions welcome.

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