Fouling plug?

wieber16 · Post by **wieber16** » Mon Dec 20, 2004 5:50 pm

I have a 1975 Merc 440 S/R. It always fouls a plug (same one every time). I replaced a bad crank seal on the fouling side, coils are good, good compression, new headgaskets, good plugs boots wires, reeds aren't cracked, carb has been rebuilt, flywheel key looks good, and I'm all out of ideas. Any help would be great.

SHewelt · Post by **SHewelt** » Fri Dec 24, 2004 12:11 am

Remive both plugs & lower piston in the side that is fouling. Then raise (rotate) until piston covers the transfer ports are covered. Pressurize the crankcase by blowing air in very slowly (not compressed air..."blow" on a piece of clean gas-line into the crankcase. If no restriction, raise piston a bit more to cover transfers. Have somebody else listen to hear if any of the air is passing to the other side of the engine...remove pipe & carb on other side & listen for air passing through. If you cannot feel any restriction when blowing, you obviously have an air-leak somewhere. This also checks to see if possibly you have a leak through the crank center seal. When this happens, the downstroke cannot build enough pressure to force the gas up the transfers. You end up loading up the crankcase with lots of gas & plug fouling can happen as the raw fuel eventually works it's way out the pipe. Another possibility is you have weak spark on that side....don't rule that out. I don't recall if that had points or CDI. If points, replace condenser & points...make sure you have good grounds to the coils.... Hope this helps

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by wieber16
 I have a 1975 Merc 440 S/R. It always fouls a plug (same one every time). I replaced a bad crank seal on the fouling side, coils are good, good compression, new headgaskets, good plugs boots wires, reeds aren't cracked, carb has been rebuilt, flywheel key looks good, and I'm all out of ideas. Any help would be great.
<hr height="1" noshade id="quote"></blockquote id="quote">

wieber16 · Post by **wieber16** » Sat Dec 25, 2004 11:45 pm

Thanks for the help but in the meantime I pulled the flywheel and cleaned up my points. Put it all back together and now I have no spark at all. I was stunned... all I did was clean up the points and re-assemble. It makes no sense. Does anyone have a wiring diagram for this sled.

Post by **Mercury** » Sun Dec 26, 2004 12:07 am

Wiring diagram emailed on 12/25.

Merry Christmas

Bill