My 2007 AC 400 starts great and idles fine. When I try to rev it, it almost dies and will not run much past idle. I have replace all the fuel lines and the vacuum line as well as the spark plug. It had set for a few months and was running fine before. I put fresh gas in it and a bit of sea foam.

What is concerning me is that if I remove the oil fill/dipstick when it is running, it blows oil out. Is that normal or might I have a stuck or broken piston ring? This thing has run perfectly for the last four or five years since I bought it used. I don't abuse it but, sometimes it does sit for a while between times of use.

Thanks for any ideas that might help with this problem.

 

You might get a compression check done, and borescope it. One weak spot that I've seen on both of my older Arctic Cats, the air intake boot can develop cracks. That can let dirt, mud even water into the motor. It could theoretically let the motor run too lean. If compression is good, I'd take carb apart, make sure the right jets are in it and blow em out, check float height , if you have an inline fuel filter, replace it.. Don't know if you have blowby, my AC's don't have dipsticks, vent crankcase into air box. I'd suspect, you shouldn't pull out dipstick when running, anyway.

 

May have went into limp mode check YouTube my Arctic cat 650v2 did it several times

 

Or your main jet is got trash in it

 

The flywheel magnets can become loose and cause running issues too

 

I've been scratching my head, haha, but one time my AC 500 was low on gas, it would idle, but stall when I gave it gas. Turned on the reserve valve and bingo, ran perfectly. Good thing, as I had about 5 miles to get home. The other thing that I did to both of my AC's was remove gas tank and dump into a 5 gallon bucket. Was shocked how much crap was in each one. I got the 500 cheap because original owner thought the motor was bad, nope, just bad gas.

 

Bet I can tell you something you'd never think it would be believe it or not but I just ran into this same problem with a 400 Suzuki Eiger 4x4 after a complete top end rebuild and clean carb mine to ran that way I finally found the problem I thought too take the muffler off (leaving the header pipe on start it up and see if it runs good and revs up then it's going to sound like **** I had a after market exhaust laying around I kind of slid up to mine and it ran better than ever in other words just slide off muffler and try that if it is I took a long sharp rod and knocked two holes in mine and still riding with a fresh rebuild it didn't really need let me know how it goes

 

Flywheel magnets is common on this model...Suzuki made an mistake be putting glued on magnets on flywheel instead of machined into flywheel...Yes suzuki made this engine also flywheel from suzuki is 100 bucks cheaper than arctic cat same flywheel