87 polaris 250 trailboss

[vwinwv]

I own an 87 polaris trailboss 250 2 stroke 2x4. I am having problems getting it to run properly. The compression on the engine is 115 pounds. The problem i am having is when i start to accelerate the engine won't take off and is blowing the compression back out of the carb. until it reaches a certin RPM then it sucks air into to the carb. and takes off. Since the 250 doesn't have reed valves i can't figure out what would cause this.

Thanks for any help!

[bradrenea]

Could be a broken piston skirt. The two stroke polaris's are a piston-port design, meaning that the piston itself acts as the valve. If the skirt is broken it will screw things up pretty good. I rebuilt one for a guy awhile back that was doing the same thing as yours and it was a broken skirt. Pull the carburetor off and use a mirror to look in the intake boot. Turn the motor over slowly with the pull starter and look at the piston to see if its broke.

Might not be your problem, but I bet it is.

[04EX]

Originally posted by vwinwv
I own an 87 polaris

Thanks for any help!

Theres your problem. Jk good luck

[vwinwv]

I finally got arround to checking the piston, the piston still looked good but the cyllinder wall where the ring gaps meet was scarred pretty badly. I guess i will have to get it bored.

[hondajoe05]

i have a 88 trail boss 250 2x4 2-stroke if you need ne parts pm me i'd love to sell this one