Case S

My Case S loads up on #4 and sometimes #2 plugs. When I remove the plugs there will be a piece of carbon between plug contacts and they will be black looking and wet. The valve job has less than 50 hours on it, at that time I cleaned the top of the cylinders and of course the head was cleaned any ideas where the carbon is coming from. The engine doesn't smoke. Most of the time it occurs when I'm idleing along but sometimes if I'm running full throtle. I'm using Autolite 306 plugs

odd ,,, chek valve clearances and push rods ,,, carbon mite be comin from intake ,it may have ancient carbon in there , the s has a thin wall of steel between intake and exhaust manifolds,,this aids in preheating the fuel but after 50yrs some of them will burn thru ,,it is hard to detect,,,,all 3 Sc s I have had here had a broken manifold when they came here , p-owner s tried everything and sold them in disgust , the manifolds are repairable ..mite take a can of ether and spray around suspect leakswhile idling anmd try to notice if it picks up a wif of the ether and pep up the rpms ,,, mite also run a quart of atf in 5 gallon of gas ,,and or LUCAS Fuel Stabilizer or Seafoam ,, All Good Products that will only continue to loosen up the carbon inb the in take and continue your problem ,you mite put a qt of atf in the engine oil to help clean up the motor ,don't put the sc to hardwork if you do ,add atf ,lite duty warm-ups , ,, If it were mine I would add lucas oil stabilizer to each new oil change ,, , also the air filter intake is probably a mess ,, take it apart and clean it ,,My Dads DC got so stuffed up with dust it would hardly run , just wheezing and whistling while black smoking no matter how the carb was adjusted , air filter had to be put in the woodstove to be burned out ,, full of oily trash from 50 yrs of pullin ..

I presume that you completely dismantled and cleaned the aircleaner ?
Loren the Acg.

John Saeli says to use Autolite 437 nonresister plugs in the S Series engines. I am going to try them the next time I need a set. The 306 is not a plug that I have heard about people using.

Thanks for the different ideas to try to solve my problem of fowling spark plugs. I"ll try the autolite 437 plugs for sure.