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motometal

XR650L-lean off idle-anyone try a smaller diameter needle?

10 posts in this topic

My XR has a lean spot just off idle. In cold weather, it's worse. Giving it more fuel screw or pilot jet is not the answer, any richer and it loads up or puffs out black smoke.

I know, the standard procedure is to shim the needle, and I have already done that. But consider this: the shimming only affects fuel mixture when the throttle is opened far enough for the tapered section to regulate the fuel flow. At low throttle openings, the DIAMETER of the needle is what matters. Shimming the needle too much just makes a rich spot at mid throttle and doesn't solve the lean hesitation just off idle.

Does anyone offer a smaller diameter needle? Has anyone tried this?

A larger needle jet may also work; not sure if the needle jet is even replaceable in this carb though.

thanks!

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I thought the XRL needle was all taper? Can't remember for sure because I haven't looked at it in a long time.

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You could be right, James. I know on our CR250s, the needle jet (which is somewhat like changing the needle diameter) is a key jetting tool.

With temps at about 40 F, there is a distinct lean spot just above idle. Even if it doesn't really hesitate badly, putting the choke on half way gives such startling throttle response off idle that I realize it is lean. With the sand on the streets right now, just pulling the choke on a bit makes the back tire break loose every time I crack the throttle in 2nd gear :)

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If it is all taper, then I think one more washer should do it.

Sure would be nice if the jets were easier to get to...that is the worst part about it.

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the needle starts out straight, but goes into a taper. There is a visible line where it changes. Looking and measuring, even at idle it appears that we are already into the tapered area. So, I may try more shimming. But, if I do have a rich spot at mid throttle, but a lean spot just above idle, I still think it would be good to try a different needle. I added .025" shim to the existing .035", and will try it out when the weather is warmer and drier. By the way, it feels like the plastic needle retainer won't allow much more of a shim to be inserted...

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The DynoJet kit comes with a differnt needle(longer and more tapered)and has 5 positions (adjustable clip).You can trim the stock needle retainer nub for more shimming of the stock needle. :)

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thanks for the reply. seems like a steeper angle on the taper would make the needle even richer as the throttle opened further, which is the opposite of the desired effect...

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high comp piston, uncorked, 58 pilot, drilled out the holes in the carb slide, disc-type aftermarket muffler

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58 pilot? Thats pretty big.I tried one with a wide open Pro-Circuit T-4 and i didn't run very well,I went back to a 55 and it runs way better. :)

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