The jettin' is to rich,if anything. Before the piston melted it would foul up the plug if it was riddin' slowly through the bush or over grown feilds for any lenghth of time.The only thing I think that saved the engine was using a good oil.I had to have the cylender acid washed to get all the melted piston off. the rads dont keep the water temp down alone,it needs the fan if you are riddin' it real hard but not travilin' at any great speeds to get the air flow through the rad.doin donuts, towin' or real tight bush trails or the engine ideling is the hardest on them If they did'nt have a problem with runnin'hot when workin'hard why put a fan on at all .banshees, tri-z, 250Rs, dont have them,since the rebuild it has ran great ,it fould a couple of plugs up but get it out in the open and run it fast for a short while usually clears it out,(plug burns a nice tan colour)if it is riddin' out in the open burns black if its been riddin' in the woods.

 

Have you checked the condition of your needle and needle jet. The needle jet controls some of your bottom end and really affects it when it gets worn. So thats why at low speeds you foul plugs and at the top speed the jet is wide open and drawing max fuel anyway. Lots of slow speed driving really wears this jet fast because all Polaris ATV engines have bad vibrations that kill carbs. A guy can count on rebuilding his carb at some where between 2000 and 4000 miles sometimes earlier if its all slow speed driving. Anyway hope your engine is over its bad case of indigestion for good
Charlie

 

Hardlydangerous, you wouldn't happen to be running w/ a 38mm Mikuni carb would you & if so how long have you been using it? I know of allot of people who could not get it jetted properly throughout the entire RPM range, & that toasted their pistons also. Just curious.
Thanks Jim Maloney 98 400 Scrambler

 

Since 90% of your riding is on the needle, that's probably the most critical carb jetting adjustment, yet the most overlooked. With the BR8ES plus it's almost impossible to get a good quick plug read after a needle clip change. Try a B8EV plug and you will be able to get a nice quick read. Run at half throttle as long as possible and shut right off, pull the plug, that will tell the story. What carb, jetting and altitude were you at when this happened?

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