im new to this form and this has got me completly stumped. i picked up a 99 polaris sport with a over heated engine. totoaly disassblemed and inspected and replaced all seals. cylinder was bored out and a westco piston installed, now for the for 4 gallons i ran through it (87 octane 32:1 with polaris 2 stroke oil) now what will happen is i start it up let it run it has a high idle. i rev it and the rpsm with jump all the way up i turn the ignition off and it still runs. i pull the spark plug wire off and it will still idle very high. pull the choke and it will die. my question is would 93 octane cause this? does this sound like a carb problem? i checked the intake boot. the one that mounts of the head and it seems everything to be ok there. im lost totaly lost! any suggestions on thing i could try? i have removed the carb and cleaned but this only happened once i added 93 octane. i will give it a shot with 87 again.

 

what you getting is called a run away motor. very common on 2 stroke boat motors. what happends is the internal temp of the chamber reaches a point that it will ignite the fuel itself without a spark. it essentially turns it into a diesel motor. it sounds like you have an air leak which is making it run lean in turn will bring the internal temps up. that along with bumping the throttle to get the RPM's up and its also sucking it more air just makes it run even more lean. i would check your bottom end seals, exhuast/intake boots. is this a 250 or 325 or 400 motor? how did the reed valves look (if it has them)
did you get the piston in the correct way? (aftermarket the size marking goes towards exhuast, OEM the arrow goes towards the flywheel)
just a few things to get ya started...good luck

 

the reed valves look good. i had the whole motor apart and replaced all the seals. sorry this is a 400 2stroke. and i installed the piston the correct way according to the instructions. i have checked the boot that holds the carb to the cylinder. it aprears to be ok but maybe i should look at it again.how can i check the bottom end? i changed all the seals while i had it apart. what are some tips i could use? and the reeds look alright, what are some things i should look for with them?

 

<div class="FTQUOTE"><begin quote>Originally posted by: Turboman412

the reed valves look good. i had the whole motor apart and replaced all the seals. sorry this is a 400 2stroke. and i installed the piston the correct way according to the instructions. i have checked the boot that holds the carb to the cylinder. it aprears to be ok but maybe i should look at it again.how can i check the bottom end? i changed all the seals while i had it apart. what are some tips i could use? and the reeds look alright, what are some things i should look for with them?</end quote></div>

If you pulled plug and engine still running (dieseling) and replaced crank seals as you say,STILL sounds like you have a leak somewhere. Seals,base gasket,intake boot cracked,VERY lean jetting causing to get hot ???

 

try starting it up and without revving the motor spray some carb cleaner around any place that requires a gasket or seal or rubber boot. go slow. if it revs up when you spray a certain area then thats where a leak is.
how does the plug look. from the sounds of things it should be very white maybe a little ashy.
you really dont want to let it run very long like that. it can melt the piston and ruin your fresh topend.

did you do anything to the exhuast airfilter or carb while you were working on it?
if you did you might need to rejet the carb (as said above) or you could just have a dirty carb

 

polaris quads have a tendency to push out the right side crank seal even after putting it in brand new. you may want to check it. and if you let the gas run low they will suck air through the fuel line and run like mad because the fuel is leaning out. the problem there is that the fuel line is too long. polaris quads are finicky but once you get them straight they are pretty dependable