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Discussion Starter #1
Hi,

I need some help trail tunning a 98 XCR 600.

    This machine has been great for top end high speed and accelerated real hard - was set up for lake running and hard cross country. But since there isn't a frozen lake this year I have dicided to "tone it down" for trail running through woods and such.
    The clutching and gearing are now stock, stock reeds, and stock jetting. (except running 360's on all jugs unstead of 380's - top end was way rich)
    Here is the problem. The pilot stage runs real crips, up to 5000 rpm - then there is a flat spot up to 5600 RPM. After that range - the sled bolts to 7600 RPM and you have to back off the throttle. once backed off, the sled stays in the 5000-5600 range.
    Plugs check out OK ant this range - light tan. At first I thought it was the transition from pilot to mid-range but when I leaned out my pilots I was getting poor combustion below 5000. And still a flat spot at the same range.
    I then tried to keep my secondary tighter using different combos but the range is still apparent.
    After talking to Polaris racing dept. - They say that there is no problem or revised jetting - But my buddies Ultra 680 does the same damn thing. I have read in other posts that most H.O triples do that as well.
   Leaning out the stock needle did nothing for that problem as well.
    I sync'd the carbs perfectly using a manometer, EGT is good, Engine temp is good. Plugs look good. But when I crack the throttle from this range I get a small hesitation (not a bog)
    Could the needle be wrong? How about changing the spark timming? Anybody done these tests?

   There is absolutely no problem past 5600 - throttle responds on demand and the sled pulls it front end off the snow about 1 foot. But you cannot maintain speed - only accelerate. Once you start to maintain RPM, the secondary opens and you are too fast for the woods.

    I know this sound like a clutching problem, but I am sure it is combustion, spark timming, Ect. I am concentrating on the engine.

I hope I have given enough info to get help, I can answer anything I have missed if you ask.
I need to fix this problem fast or else I will need to take my wifes "formula DLX" on my next trip and my buddies will laugh at me - so please help.

Thanks in advance
 
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