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post #1 of 9 (permalink) Old 04-11-2010, 07:26 PM Thread Starter
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92 XCR 440 Jetting

It's actually a 91 XC-400 but it's basically the same as the 92 440 XCR. I bought it from a guy I work with who had it for his kids to ride around on and says it always ran great. Anyways the sticker under the hood says the main jets should be 280's. Upon cleaning the carbs I discovered the PTO side is a 350 and the mag side is a 290. Why would this be? Should I change them both to 280's? It's stock as far as I can tell from the clutching.
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post #2 of 9 (permalink) Old 04-12-2010, 10:13 AM
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Often a fan cooled engine is jetted with different sizes because the one cylinder (pto) runs hotter.

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post #3 of 9 (permalink) Old 04-12-2010, 06:32 PM
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neither of the sleds he mentioned are fan cooled...

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post #4 of 9 (permalink) Old 04-13-2010, 06:09 AM
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But he is right on the PTO side running hotter than the mag. If the plugs are both a dry brown color, leave it. If the 350 side is all black and sooty, go down a couple sizes.

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post #5 of 9 (permalink) Old 04-13-2010, 06:20 PM
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Quote:
Originally Posted by smallengineguy View Post
But he is right on the PTO side running hotter than the mag. If the plugs are both a dry brown color, leave it. If the 350 side is all black and sooty, go down a couple sizes.
Ya I know that, I just figured Id mention that neither of them are. Seems to be there are a lot of one liner answers coming from people (not JUST RJ), that are so quick and simple they really do nothing to help the original poster. (dont take offense to that RJ, none was intended)

I think this person was looking for a little more in depth of a response to his question, and I wish I was up to speed enough on jet sizes to give him an educated response. But I dont like to give answers which I dont know are 100% factual and true. But back to topic, doesnt a 350/280 jet difference seem a little extreme to you SEG? Maybe its not, but I always thought jet differences for PTO/MAG and for the center cylinder in triples was usually only about 1 or 2 sizes. maybe a 280/290 split or something. Please chime in and correct my probably incorrectness, Im sure the OP would love it.

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post #6 of 9 (permalink) Old 04-13-2010, 11:07 PM
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Well, first off, I was operating on the assumption that they were fanners.

Two, depending on the elevation and pipes, you will have more heat from the PTO cylinder due to pipe placement/configuration.
A single pipe setup will usually have a wider difference between the carbs than a multi-pipe setup.

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post #7 of 9 (permalink) Old 04-14-2010, 12:25 AM
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One jet size diff. is about as much of a split you would want any more than that and yor performance would suffer.
I'd put 290s in bolth, if that cyl. had good plug colour.
If it is running rich in one cyd. clean the carbs set them up ,do a compression check
then if it is still fouling plugs go one heat range hotter for that plug.
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post #8 of 9 (permalink) Old 04-14-2010, 09:01 AM
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^^^^^^^^^^^^^^^^
Sloppy way to fix the problem.
Keep the plugs the same and the recommended heat range.
Fix any fouling problems by finding why it is doing it and adjust jetting/slide needle height to clear it up.

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post #9 of 9 (permalink) Old 04-14-2010, 09:02 AM Thread Starter
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Ok thanks for the replies. Someone on Snowmobilefanatics mentioned maybe the PTO side crank seal is leaking so someone jetted way fatter to compensate. I'll have to check that out, otherwise I'll switch them both to 290's and watch the plugs.
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