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I have a 94 sportsman 400 that i cant get running right. It idles fine but when you start driving it it falls on its face and starts backfiring and popping then it will start moving again and then start backfiring again. Once and a while it will suddenly run great and have no issues until you shut it off and try to ride it later. It also has a hard time starting and will only start if you depress the throttle. Today i noticed that when i took the top of the air cleaner off there was fuel coming into it so i checked the floats and float arm and they are both good and the carb is clean and it has a new spark plug. I also turned the fuel on and depressed the float arm with my finger and no gas was running out while i had it depressed. The guy i bought it from couldn't get it running and may have tampered with the carb but i am not sure. Does anyone have any ideas of where to look or have had similar problems? Thanks
 

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I had a sled that did that. It was the stator. Just a guess tho. There is a thread on here somewhere on how to check the ohms I think.

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One guy posted he had a similar issue that was due to a loose grounding cable one and and again when the insulation got bad on a wire and taping it well fixed the running issue.

As with all gas engines you are looking at an electrical or fuel related issue. It can be really hard to trouble shoot and one can even have both issues at the same time.
 

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Does that model have the CV carb? if it does look closely at the diaphragm for any tear or holes from being pinched when it was reassembled. It sounds a bit like the air isn't always getting in the motor and the gas coming into the airbox,it is also a sign the engine is trying to suck air but can't so it draws a bunch of fuel, which blows back into the airbox.
Fire hazard from a backfire is extremely high in this situation so keep an extinguisher handy when playing with it now, I saw a garage burn down from a backfire with fuel.
 
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