Mercruiser 470 (120/140) Plugs foul if below 10 mph for 10 minutes....WHY????

[djfam]

I have a 1982 Mercruiser 470 that runs like a horse, but at 10 mph or less for 10 minutes or so (like in a no wake zone) the plugs foul. I'm trying to figure out why. Plugs have been replaced as has all electronic parts such as points, wires and ignition (which is now electronic). Am I looking at a possible carb issue, too rich or lean condition, or something else.

Thanks for help.

 

[Don S]

Re: Mercruiser 470 (120/140) Plugs foul if below 10 mph for 10 minutes....WHY????

Am I looking at a possible carb issue, too rich or lean condition, or something else.

It's possible, did you re-adjust the carb mixture after setting the dwell and timing after installing the new points? All three have to be done you know.
Is the choke working propely????
Have you done a compression test?
What is fouling your plugs? Fuel, Oil, Water??????

 

[freddyray21]

Re: Mercruiser 470 (120/140) Plugs foul if below 10 mph for 10 minutes....WHY????

if it is only doing it for ten minutes I would suspect the choke. It shouldn't take 10 minutes running to warm it up and pull the choke off. Pull the flame arrestor off and see if the choke is sticking closed. In my experience if a carb is adjusted too rich it will have the same symptoms all the time (worse when cold) not go away after 10 minutes.