1980 Mercury 70 hp fouling plugs

[noahnsteph]

I'm going tomorrow to look at a new motor for my boat. It's a 1980 Mercury 70hp that the guy says was fouling the #1 cylinder. He says the marine shop told him it needed carb work and timing adjustment. What causes plugs to foul.

He's asking $400 for it.

 

[emckelvy]

Re: 1980 Mercury 70 hp fouling plugs

Better take a compression gage with you and if the readings are more than 5 psi difference between cylinders, run! This motor is well-known for cracking the block when overheated, and even if the block is intact, #1 piston usually suffers a lot due to carbon buildup or other issues.

Plug fouling can be a number of things, but remember the Merc electronic ign system puts out a heck of a lot of voltage so unless it's totally gunnysack, I kinda wonder about the 'plug fouling' reports.

Small possibility there could be a stator issue and that'll cost you a couple hundred to fix, for example.

Probably something far worse such as water intrusion or who knows?

Anyway, check it out carefully, $400 for a pile of 3-cyl parts is no bargain........ed

 

[noahnsteph]

Re: 1980 Mercury 70 hp fouling plugs

I'm planning on bringing the compression tester for sure. In keeping w/ positive thinking could the plug fouling be as simple as improper fuel mixture. I seem to recall too rich of a fuel mixture causing plug fouling.

Other than the compression what other tell tale signs of trouble should I look for?

 

[Kev144]

Re: 1980 Mercury 70 hp fouling plugs

the general rule of thumb is that the PSI in each cyl should be no less than 10% difference. and should be 90ish +, more or less over 100 on each again 10% difference. FYI, a stator only cost me 100 bucks plus my time to do it. Not very long as i know what im doing and have the tools. (150 merc Black max)