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250r Fouling Plugs at Idle

5K views 8 replies 5 participants last post by  FTZPoweredBlaster 
#1 ·
My buddys 86 250r keeps fouling plugs at idle. As long as you're riding or moving, even at a slow pace it runs fine and will not foul the plug. If you let it idle more than a few minutes, it's toast. It's an unported 86 jug, standard bore with a wiseco piston, short rod crank, cool head w/ 21cc dome, atc head gasket, boyesen pro series reeds, fmf fatty pipe & silencer, keihin 35mm a/s carb-155 main, 48 pilot, needle in the middle, pilot screw 2 turns out. Stock air box w/a uni filter, lid off, amr coil, b8es plug gapped at .018". We just replaced the stator with a oe unit. He tried a b7es plug saturday and said it ran better than ever and didn't foul the plug. Should he keep running the b7es or drop the pilot jet to 45 or even a 42? I don't know what else to do to keep it from fouling plugs. :Banghead1:
 
#3 ·
Klotz super techniplate at 40:1 on 93. Amr makes aftermarket coils, cdi's and graphics kits. The old r ignitions aren't that great. They don't run with the plug gap opened up. It's got 185-190 psi last compression check.
 
#5 ·
agree's with jared..... try bumping the pilot jet down one size at a time and see where that gets you. adjusting the pilot screw accordingly.
 
#6 ·
I'd recommend dropping the pilot one number and see what it does. 48 already sounds a little bit lean, but you never know. Have you ran a leak down test to ensure its not sucking trans fluid or anything?

There really is no reason that the motor should need to run a heat range 7 plug. Honda recommends 9 series range and if it needs 2 more ranges hotter to run right something is up.
 
#7 ·
Yea we just rebuilt it a month ago...had to replace a busted left side crank half. I know the clymer manual says 86-87 came with a 48 pilot. 88 had a 45 and 89 had a 42. He's got a 45 ordered so we're gonna give it a shot. The bike runs strong...it can hang with my banshee for a short distance but the r does get better traction in the dirt.
 
#9 ·
He had been running a b8es but went to a b7es...said it ran great and didn't foul the plug. We're still gonna drop the pilot jet down and go back to the b8es. I'm afraid the b7 is gonna be too hot and hurt the engine.
 
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