Help with 2000 polaris scrambler 400 4x4 !
 

hello everyone. i am new here and this is my first post. i am having trouble with my scrambler. a little background on atv. i bought off craigslist from a guy that new nothing about it. it has ran somewhat ok for 1 month until last week it was at idle and the engine seized. i took it home. pulled the carb, reed spacer, and reeds out and saw no scratches on cylinder walls or piston. i sprayed sea foam lubricant in cylinder and allowed to set over night. now it starts again but runs terrible. here is what i know on engine. it has a AAEN head, v force reeds, hot seat exhaust,mikuni 42mm?? carb. im sure im forgetting some things. compression test showed 120psi at first now its 95 psi. i have unhooked the oil injection system thinking that it had failed. i have not installed block off kit. any tips or suggestions on what to do next is greatly appreciated. thanks everyone

95 psi isn't good. At least take the head off to see what's happened.

OK. I plan to do that by the weekend. I will update. Thank you very much (old polaris tech) for the reply

ok i took the head off last night. ive never been into one of these 2 strokes and it seems there are 2 rings. one of which (the bottom ring) spins and moves around freely. it looks ok. the other ring (top of piston) seems like it is stuck or molded to the top side of the piston. is this correct? also the top of the piston is really rough and not smooth like normal pistons i have seen before. i have pics but cant seem to figure out how to post them. cylinder wall looks perfect. piston looks good except for the top of it. is this correct and any other suggestions?

Probably over heated, or running lean,air leak,etc and partiallly seized. The ring's probably seized to the piston. Tear the cylinder off and look at the piston and cylinder especially on the exhaust side.

cylinder looks good. no scratches or anything. the piston looks ok on the side however the top ring is seized. it should move freely like the bottom ring correct? and also should the top of the piston be smooth or rough looking? ill take a closer look at the exhaust side when i get home

Top of piston should be smooth!!! What's probably happened is either bits and pieces from the piston/rings or lower rod bearing or crank bearings have "peppered" the top of the piston or it's just gotten super hot! Check the head and see if it looks rough also. And yes the rings should move freely on a piston. You can only guess until you check it out thoroughly.

ok. seems the motor is coming out and torn apart for full inspection. i will update when i get it apart.i should probably take it to someone who knows fully what they are doing but i would rather learn it myself. hopefully ill have her out and apart by the weekend. thanks again

Check the water pump for grooves in the shaft. Do you know where to add oil for counter balancer? Should be underneath the seat, long flat blade screw driver will get the dipstick cap off.
With all the hi-performance parts on that machine and the previous owner not knowing much about the quad, well lets just say, you're doing it right by yanking the motor out. Cylinder boring won't be bad, unless it needs a new sleeve. If you got bottom end rod play and can see bearings are shot on crank, then the rebuild price goes up significantly. Splitting cases requires some specific tools. Good luck and keep us posted

It sounds like you might be running lean if a ring was melted to the piston. Do you have any port work done to your cylinder because the 42mm TMX is a big carb to be running on a stock quad considering the factory carb is only 34mm? If you have a stock cylinder then you would probably be better off with a 38mm TMX. It also sounds like you might be having some detonation problems. I would check out the dome in the head for pitting also.

I wouldn't be afraid to tear into the motor yourself and check everything out as long as you have a good manual. Two stroke motors are really simple to work on. You can always check out some videos on YouTube before you start just to get an idea of what everything looks like.

Here's some pictures of the dome in my Billet Aluminium 2 piece head and my spare cylinder that I run on my Polaris.

http://imageshack.us/a/img405/5628/p1010232y.jpg

http://imageshack.us/a/img21/1693/newhead002edit1.jpg