I have a 400 polaris scrambler, 2 stroke. It starts and runs fine until it warms up then it starts sputtering. I have rebuilt the carb, and still have this problem. Replaced the reads and still same problem. You can tell were it has some seapage around the head. Please help. Thankyou for your input and time. Madvmax

 

Check your battery was told a bad or weak battery on 400's would cause a sputtering when warmed up.

 

Do you know how a bad battery would cause this problem. Thankyou

 

do you have a spare spark plug,that you can check the spark when cold, then check it again when it starts acting up.
shouldn't be any seepage on the head, you could check the compression also

 

Also what do you mean by checking the compression. when its hot and cold. What about spraying carb cleaner around the head when its hot like you would on a car for a vacum leak. Thankyou Madvmax