I just rebuilt the top end on my Polaris 400 scrambler for the second time. Last time it only ran for 4 hours and the rings melted to the piston. A self proclaimed Polaris mechanic told me it’s running to rich and to turn the air fuel mixture screw all the way in and then back out 1 and 1/2 turns, so when I rebuilt it this time it’s running like crap no matter what I adjust the air fuel mixture screw at and it has oil in the exhaust pipe? What’s up?

 

if it's running too rich, it would not have metaled the rings. too rich means it's getting to much gas and not enough air. sounds like it was the other way around. when your bike runs way too hot, not enough gas and too much air, is when you can have a melt down or seizure. is your oil pump hooked up or do you premix and have a delete kit on/ if it's not getting enough or any oil injection it would also cause a seizure. do you have the correct size jets in the carb? pull the spark plug out and look at it. if it's covered in oil, your getting too much and same if it's gassed soaked, your getting too much ogas meaning it's too rich.

 

I bought my 400 scrambler about two years ago and the engine was tired so I sent it to a gentleman in Texas who rebuilds Polaris engines and he had me premix oil in the gas during break in along with the oil pump. My nephew put it all back together but never connected the oil line to the intake boot so once the oil in the first tank was gone it was running straight gas which as you might have figured out seized the rings to the piston and it lost all compression, so I bought a kit that included the cylinder, piston, rings and gaskets. I rebuilt the top end and added oil to the gas and hooked up the oil pump. It rand really good for about three hours and then it seized the rings to the piston again so I got a replacement cylinder and all. The mechanic that rebuilt the motor in the first place told me to check the adjustment on the carburetor and that it should only be 1-1/2 turns out so I did that before I tried starting it, by the way it was 4 turns out at that point. Now I can’t seem to get it to idle right no matter where I set it, I can get it to idle for a few minutes and then it stalls. Also I have to choke it every time to get it to start even after it warms up and when I rev it up it stays revved up for a few seconds before it slows back down?

 

4 1/2 turns is way off. I would say, it's closer to the 1 1/2 turns. you may want to check for an air leak by what your describing. if you didn't have the oil pump adjusted i might recommend deleting it and just running premix to be safe where you have 2 burn downs already. as i mentioned, check the plug to see what it looks like as it will tell you if it's burning rich or lean or getting oil fouled. using the enrichener (choke) is some thing you should never have to do. i would check all the adjustments on the carb to make sure it is set up correctly and again make sure there the carb boot is on and there is no cracks any where that is lets air in from the outside which will some times make the engine rev as you explained.