possibly bad coil on kx250? almost like plug isnt staying hot

[jetpilot773]

i have a 1995 kx250 i have been messing with for forever. i was running it on 2-stoke valvoline, 32:1 mix. the thing would run great for about 15 mins then die like it was fouled. i cleaned off the plug changed the gas and put a 40:1 mix of castor 927 (expensive stuff) and it did the same thing. i got a new plug wire and a new spark plug but its still happening. could the coil be bad??? somehow not staying hot enough to keep the plug firing consistantly?

 

[kshackleton]

i have a 1995 kx250 i have been messing with for forever. i was running it on 2-stoke valvoline, 32:1 mix. the thing would run great for about 15 mins then die like it was fouled. i cleaned off the plug changed the gas and put a 40:1 mix of castor 927 (expensive stuff) and it did the same thing. i got a new plug wire and a new spark plug but its still happening. could the coil be bad??? somehow not staying hot enough to keep the plug firing consistantly?

The plug is heated by engine combustion...not the coil. Coils can have a failure mode whereby they function fine until they warm up, then they fail.....more likely though, I would suspect jetting.

What plug are you running?

 

[eatf001]

Hi there

Do you have any info on the electrics on a KDX220SR?

Thanks

Terry

 

[jetpilot773]

The plug is heated by engine combustion...not the coil. Coils can have a failure mode whereby they function fine until they warm up, then they fail.....more likely though, I would suspect jetting.

What plug are you running?

plug is a NGK B8EVX i beleive.
you said the coils can function fine until they warm up, then it goes bad. would riding for like 10 mins then the thing just dying be a symptom???
it just quits almost like it runs out of gas or the plug fouls or something.

i find it hard to be the jetting because it was running just great before until this problem.

 

[kshackleton]

plug is a NGK B8EVX i beleive.
you said the coils can function fine until they warm up, then it goes bad. would riding for like 10 mins then the thing just dying be a symptom???
it just quits almost like it runs out of gas or the plug fouls or something.

i find it hard to be the jetting because it was running just great before until this problem.

I'd be thinking the coil too.....if the shutdown is that rapid and it has been running fine to that point. You could test it by running it until it fails, remove the plug wire and plug in a spare plug.....touch it to the engine block to ground it and kick the bike over.....does it spark? No.....bad coil......or the pickup coil by the flywheel could be failing also when it heats up....for that matter, it might also be the controller too.

If your tests show that this is a heat related failure killing the spark....let things cool down, then with the test spark plug attached where you can see it....heat up each suspected component with a hair dryer on the highest setting and kick the bike over to see when the spark fails.


Ken