No response to first post so I'll restate the problem. 1997 FLHT. 62,000 miles. Front plug fouls, rear plug OK. Parts replaced so far with no help:
1. Plugs. RN12YC. Also tried RN14YC in front. The hotter 14 helps a bit.
2. Plug wires (twice). First Magnacor, then Accel.
3. Ignition module. Swapped Screamn' Eagle back to stock module.
4. Carb rejetted to lean (Mikuni HSR42). No help- now running #70 pump nozzle, #25 pilot, #97 needle, #165 main.
5. Coil
6. Added disks to mufflers (White Bros E-series). Now running 12 disks.
7. Intake manifold seals. They were leaking.
8. Also tried different brands of gasoline.

Fouling problem continues. Any ideas? Might this be a question for the "Electrical/Ignition" forum?

 

I'm no expert by any means but looks like you've changed all the normal things that could cause this. Is the plug fouling wet or dry? Deposits arcing across electrode or not? Only thing that comes to mind that you haven't tried is you may have a bad head. Seals leaking etc. Is she burning oil at all? May want to do a compression check and leakdown just to see what the condition of your head and rings are.

r/ George

 

Fouling is sooty and dry - also exhaust blows black smoke. Does not burn oil. Did a compression test - 150 both cylinders - but not a leak down. Fouling involves plug body, porcelain, and center electrode, but not ground electode. At this point, I am thinking that you are right, that something is going on internally. Only other thing that comes to mind is the ignition magic in the "cone."

An interesting characteristic is that the motor tends to run smooth and strong for the first 10 miles or so, then it starts a vibration of sorts and soon the plug is fouled. Even so, it will rip thru the gears at WOT, but settle down to a cruise and the missing starts again. So there appears to be no loss of power except for the fouled plug.

Thanks for your help on this.
Ted

 

TG580, this may be a shot in the dark but where is the accelerator pump nozzle pointed? Is it possible you are getting fuel from the accelerator pump into the front cylinder only? Since your front plug is sooty its an indication of a overly rich condition. Try removing the air cleaner, start the bike and watch the accelerator pump "squirt" while opening and closing the throttle. Is there any gas coming out of the accelerator pump nozzle when the bike is just idling without twisting the throttle? Post back what you find.........BG

 

BG- Chk'd accel pump nozzle. Despite my careful(?) aiming when installing, it was indeed squirting a fair amount toward right of center. I reaimed it to hit the needle jet. Makes sense that this could contribute to fouling front plug. A shakedown cruise is called for here. That probably won't happen for about 2 weeks as the weather is RAIN now and then I leave to get in next winter's firewood. Standby for an update. Thank's for the suggestion.
Ted

 

Just a thought. You can check the coil by reversing the wires and see if the trouble goes to the rear cylinder. I'm guessing you still have the wasted spark system and haven't changed to single-fire. Coils have been known to fail once they warm up. Just my 2 cents.

 

Good idea and I wish this would have occurred to me a while back. Original coil bench tested OK so I reinstalled it -should have tried swapping wires. Later I replaced it with new OEM coil and that seemed to do the trick, but I had the carb so leaned out it was hard to say what the true result was. Now the problem is definitely recurring, following rejetting to "normal." So I might have a different problem (rich jetting/accel nozzle) producing same results as a weak coil. Gotta ride it with the accel pump nozzle reaimed, but I'm not optimistic. Thanks for the suggestion and I'll try it even thought I did replace the coil. Might have swapped bad for bad - who knows?

 

George- It quit raining so I took her out for a spin. No change - still fouling. But at least the nozzle is aimed OK.