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Discussion Starter #1
i have a 97 xc 440 it startts fine but when you give it gas its boggy and backfires through carbs. i know its running rich but it was running fine 5 mins before it starting acting up. I checked the compression both are at 127 lbs. Main jets are 200 and choke cables are readjusted. It kinda sounds like a short but i can not find it. About what jets should i be running. Any input would be greatly appreciated and thanked for.
 

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Clean your carbs, they may be icing up. Add a bottle of Iso in your fuel tank and top it off. Don't let your tank sit less than half for more than a week otherwise condensation will take over.
 

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My Ultra was doing the same thing on Saturday I discovered on Sunday that my wiring harness was rubbing on the jack shaft.There was one wire which was bare and the it was shorting the cdi box and making her back fire but she's all fixed now [:D]
 

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backfiring through the carbs is a sign of lean combustion unless this is an electrical issue. Could be that you have broken pistons, plugged carbs, or wrong carb adjustments.
 

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Discussion Starter #6
I cleaned the carbs twice with in 20 miles between cleaning. I just put the sled together. I bought a 98 xc 700 for 150 bucks but the crank had busted. So I had my 97 xc 440 motor just sittin there so I customized the motor mount and dropped it in. Both Wiring harness's were pretty much the same. After i got done w/ the sled i took it for a couple rides up the road and it was running very strong it kind of suprised me. Then a buddy went for a ride and sounded like he fouled a plug. When he came back I changed both plugs and it didn't come outta it. Both plugs have spark.
 

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Discussion Starter #7
I figured it out. The guy I bought the chassis from didn't tell me the gas was 4 years old so I drained the gas ran the lines dry. Put in some new gas w/ isoprople and it started running good for about 10 seconds and then started getting boggy. Pulled the carb apart the clip fell off the needle and was stuck down. Put it back together now she runs like a champ!!
 
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