irratic running

Well, im stumped.

My 1985 XC500cc starts fine, runs fine for about 3km (2miles), then just as its warm if i lay into it it starts to splutter, this gets dire real quick, to the point of almost dying, you have to jiggle the throttle from closed to 1/4, to get it home.
l don't think its fuel related, the carb is fairly new.................and ive clean it 5 times, also it backfires and smells of fuel, damp plug, damp tailpipe. lf i leave it a bit, it will do the same thing, start fine, go to shite in 3 km.....................................a day and a half later im done!!

Been through the wiring, cleaned terminals checked for kinks. all good.

ls there anyway to check the coil/stator with a multi meter??

Cheers

have i missed anything?

I think in the parts and services there is a link to Vance Smiths Motoplat repair and troubleshooting. Sounds to me like ignition with the backfiring. Coils get hot from use and that may be whats happening. Coils can be difficult to test because of a static test ca be alot different than a running test, I keep a known good spare for that reason! I have used a heat gun and checked the coils before on one that would quit after it warmed up/rode a bit. Good spark untill I heated the coil to 100deg.F and then spark would dissappear. Hope this helps. Scott

Hello Scott.

Thanks for that,very helpfull, i had a feeling it was the coil, but no way to test. l used the 'Vance' test as directed the stator tested good and the resistance reading that should be 5.5k-5.6k ohms is 10.23k ohms on the coil, so i guess that's toast, time for another!

.................huskydoggg where for art thou huskydoggg

sounds like a bad upper coil, or a bad kill button

......the plot thickens.

Thanks for the tips guys.
Well today i pulled out the coil, before i tossed it i removed the plug cap for a spare and thought i would test the coil again while i was at it, surprise surprise the coil tested good, so i guess it must of had a cap with a resistor???

So, i put a different cap on and it tested good, so i will put it back in and see what happens tomorrow!

lve blown out the kill switch with some air, maybe i can isolate it when i put it back together so i can rule it in or out.

iv started to put a dab of elect grease on the inside contact of my kill buttons, that seems to help them last, and keep the crud from building up.
iv had more then one spark plug cap go bad, be happy, most the ones i have had go out, were at the bottom of a big hill, or the middle of a creak someplace, far away from the truck.

...........................well, it was the plug cap in the end!

Never crossed my mind to check, good one no resistance, this bad one 5.5k ohms resistance.

For some reason this new cap also leaned the bike out slightly, (about 1-1.5mm on the porcelain)

So, thanks for the tips guys. My future SOPs will be to check this first................before pulling the bike apart, several times!