I have a 2006 Polaris 400. it was running fine then just cut off. Turns over fine but wont fire

Have you checked the Crankcase seals? I have 2 Big Bosses with 250's. 1989 + 1992

Both were terrible at starting and idling....after much troubleshooting I finally changed the crankshaft seals. (Which btw looked fine from the outside!) machines can be Cold now and will start 2 or 3rd pull with the cord now. Idle perfectly.

Also the oil injection system stopped working intermittently. Machine would just quit.....crank and crank it forever. So I just started using 32/1 mix and unhooked the Oil Injection cable from the Throttle.

When was the last time it ran.

You might try to ask someone to help on the ATV web site below:

https://atvconnection.com/forums/polaris/330956-year-my-sportsman-400-4x4-1997-a.html

Sounds like the float bowl in the carb is sticking, go get a can called "Sea Foam" from your local parts store add about half the can to a full tank of gas take it for a good ride it will clean out any gunk and deposits in the carb and make it run good again i had the exact problem you are talking about with my wife's Suzuki Eiger 400 i let it sit for 5 months and it caused the carb to get all gummed up i ran Sea Foam in the gas and it runs like brand new again after riding it for about 45 mins.

most likely a fuel issue. has it been sitting up ? if so if its got a carb it prob gummed up, pour some seafoam into the gas tank with fresh gas and run it, try and keep it running with the throttle, it might clear some varnish out the carb if it not too bad, if tht dont work and it is a carb engine then the carb will have to be removed and cleaned. if it a FI engine then you got a bad full pump more than likely

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Check valve clearances. Gas coming out back of carb could be compression

This is a timing issue. The crank and cam are out of time. It might be excessive wear,

Have you checked the Spark Plug ? No Spark & No Fuel means not going to start and run. If you are getting fuel then your Spark plug may need to be cleaned or replaced or even re-gaped. Spark plugs have a tendency to get fouled out. Meaning oil gets on it and it can not throw a good spark. If you do have a good spark then check the choke and or the float in the carb.

Thanks for allowing my in-put!

the fuel doesn`t pass, the fuel jet clogged ,try to cleaned the carb very nice ,allow small jet and little orifice nozzle in a (soaking bath cleaner.( OVERNIGHT)Do not use wire or .wire brush

Sounds like the carb,has it been check after its test and tune ?