Why do I constantly foul my top plug ?

[daviea32]

I've got a 1976 Mercury 650, 65 horse, 3 cylinder motor. It sat for 3 years without running. I replaced the trigger and switchbox, that was the reason it was down for so long. Now I keep fouling the same plug, the number 1 cylinder. When I pull the plug out it has a grey, gritty deposit on it. Could that be my piston or cylinder walls getting chewed up? Or is it just dirt and grime from it sitting for so long? I've taken the carbs off and apart and cleaned them good so I know that isn't the problem. I've done a compression test and it cheked out ok. Could it be a timing problem? A local mechanic said to retard the timing 2 degrees and run high octane fuel. Does this sound right to any of you? I've been given so many ideas, I just want to cover all the bases. I'm going broke with this thing. Any information you can give me would be greatly appreciated.

 

[petryshyn]

Re: Why do I constantly foul my top plug ?

Doesn't sound good.<br />>Did you do a compression test?<br />>Did it have a strong telltale stream when running?

 

[jwhite]

Re: Why do I constantly foul my top plug ?

grey, gritty deposits? Sounds like piston to me. Do a compression check! Did you clean the carbs after sitting up for 3 years?

 

[sho305]

Re: Why do I constantly foul my top plug ?

I would get a flashlight in there quick like and take a look at the cylinder if that is metal on the plug. See if it is scored up. That is usually from a lean condition. Compression test will tell you too. If it is hosed I am surprised it would run long/well.

 

[Beernutz]

Re: Why do I constantly foul my top plug ?

Check the mainjet in your #1 carb. It's probably clogged (partially?) with sediment. It most likely will not clear itself out. She's running lean on that hole, and that's your piston your burning up. I'm surprised that it hasn't seized!<br /><br />Also, make sure you got the float installed properly in that carb after you put it back together the last time. A low float level will cause the same problem. If it got bent, replace it. <br /><br />A leaking top main seal can also result in a lean condition in that cylinder.