Soot fouling front plug on 35 Chief

[35chief]

So the front plug has been fouling with black soot every 30 to 50 miles. The rear cylinder runs clean. This has become a bigger problem over the last maybe 2000 miles over a couple years. There is no oil on the plug, just black soot. , did rings and pistons on both cylinders 5000 or so miles ago. I have maintained the ignition system as it was when I got the bike 32 years ago. Long story short someone cut the magnet off the back of the Edison Splitdorf and it uses the points to fire both cylinders at the same time using a 6 volt coil,,,, so I can swap wires front to back and around, makes no difference, front plug fouls. I know it is a jerry rigged system but it has worked flawlessly since the 70's. With the T intake manifold and equal compression it should not run one any richer than the other. No vacuum leaks either.
Would a burned exhaust valve do that? Any clues? Thanks

[23JDCA 808]

Maybe run a hotter plug in that cylinder. I had a car motor that fouled the #4 plug; I put in a hotter plug and it ran fine. Work into the hotter range by steps; don't just throw the hottest plug you can find in there.

[T. Cotten]

35Chief!

How did you test for vacuum leaks?

I would predict a leak to the rear cylinder.

....Cotten

[35chief]

I have always run Autolite 303. I will gladly try any other plugs you all can suggest. Parts stores are useless and local bike shops are no better here.
I have used brake cleaner, propane and water via pin point squeeze bottle around head gasket and intake manifold to rule out. I just can not figure how , with good spark, side draft carb in to a T manifold ( equal opportunity for air fuel mixture) if a lean condition was the problem that would be easier to trouble shoot, and no oil fouling I am baffled. Thanks for your time and giving it a thought.

[T. Cotten]

35Chief!

I suggest that you leak-test your manifold assembly more thoroughly: http://virtualindian.org/11techleaktest.html
Bubbles will show leaks that the common method often misses.

Let us know how it goes,

....Cotten

[35chief]

Thanks Cotten, great post and thanks for reminding of that site, great help.