fouling plugs

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Oct 12, 2003
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#1
ok, just got back from trip..and fouled 3 plugs in a day and a half. No misses, perfect throttle reaction..the bike screams down the open striaght aways..no performance problems.
Twice when I fouled the plug, the bike refuesed to keep running and died out. I am running Water pumper for my 2 stroke oil...mixed at 40:1. I have a uni air filter with a pre - filter over that. NGK B8ES spark plug...never gap it though.

I hate to mess with the carb settings when it runs so well, but the thing left me stranded on this trip waiting for a tow strap when it fouled the last plug in the woods. If i do not keep the thing screaming...and their is ANY idle time, it fouled. Anybody dealt with this....I love the bike, but am about to buy a four-stroke :(
Ryan

89 WR250
 

Faded

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#2
Originally posted by rwhite65
...and their is ANY idle time, it fouled.
Sounds like your pilot/airscrew setting is rich. Try the next smaller sized pilot jet and see if this helps any.
 

RM_guy

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#3
Did it just start doing it? If so then eliminate everything else before messing with the jetting. You might be leaking oil through the right crank seal.
 

Wolf

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#4
I had the same problem. My bike ran great and then, out of no where, started fouling plugs. Then, coincidentally, my trials bike did it too!
The common denominator...same batch of gas...bad gas...really bad gas.
 

RM_guy

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#5
Yeah sometime I get real foul when I have really bad gas...er...um...what were we talking about :confused:
 

YZThumper

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#6
Same thing happened to me on a YZ 250 I owned. Bike ran great for 2 years, perfect carbureation, throttle response, and no changes to anything other than top ends. One day out of the blue it began to foul plugs. Usually this happens to guys who are lugging it while riding tight trails, but this happened to me even when the bike was being ridden flat out. Turns out the crank seals and bearings went south and it was sucking oil which caused the plugs to foul.

If you haven't messed with the jetting, it's more than likely not the jetting. Take the stator cover off and check for play in the crank to see if the bearings are truly shot.
 

Jaybird

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#7
Crank seals and bearings for a 14 yr old bike is alot cheaper than a thumper.
 
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May 14, 2004
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#8
That happened on my 1995 WR250. My transmission vent tube got pugged and the pressure build up forced tranny fluid past the seal and fouled the plug. Once I cleared out the vent tube, all was right in the world again. :)