random plug fouling-cold header

[nutsandbolts]

Hello all,
This might be tricky to answer. here is the back story;

Valve shims set, carb dipped, rebuilt completely & vacuum sync'd by dealer, new orings on intakes, new intake box boots, new exhaust seals, new points, new condensors, timing checked and set by dealer, new plug caps, coil relay modification done.

Bikes starts and runs fantastic when it runs. It randomly fouls a plug about 120 kms into a new plug.

I can't think of anything but compression and a piston/ ring issue. Before I tear it apart, any suggestions would be greatly appreciated.
Thanks in advance,

[SqDancerLynn1]

If it is oil fouled you may have a bad valve seal or a stuck oil ring. How many miles have you run it ?
if it is sooty black it may be choke plunger leaking ????
What plug does it foul ? If it is # 3 it hooked to the petcock so that could be a problem ???

[nutsandbolts]

Thanks for the suggestions,
53k miles
oil fouled
It is never number 3 consistently, varies. your suggestions lead me to think the engine is going

[trippivot]

I have a couple ideas that make more sense than jumping to expensive conclusions..

by doing a leak down test you can determine if it is fact oil control or ignition resistance or fuel balance / control.

I like to start with cheap and easy - then work towards complicated and expensive.

plug cap reisitance - plug heat range- fuel control -- on the choke for way too long?


re check the simple stuff.

[Big T]

If it's random, it definately not a sign the engine/compression/rings are bad.

How often is the fouled plug #3?

[nutsandbolts]

thanks folks,
I completely forgot about a leak down test. I'll do that first then recheck my resistance and maybe the coils too though I've been told those rarely go.

I've replaced the 1,2&4 plugs about 4 times, the number 3 maybe twice. Plugs are on hotter (7's) than stock 8's.