Plug Fouling Causes

I need to pull some plugs again and check out whats going on.

My question is - is plug fouling common and why does it happen?

Also, if my exhaust manifolds (where they connect to the engine) were extremely loose and loud, could that contribute to plug fouling?

A clogged air filter,incorrect carb settings and/or weak ignition system all can add up to sparkplug fouling.

Have you done a compression test and have the valves been adjusted lately?

Hopefully it's not a broken oil control ring on the piston(s)as this can also lead to fouling.

Have you switched the brand of sparkplug from what worked in the past? I've heard good things about the denso brand of plug(used to be called nippon denso).

Well the carbs were just redone so I'm hoping there's no issue there. The plugs havent been replaced since, though.

The previous owner is responsible for the current plugs. I think he had said something about fouling but I don't remember.


Its going to be a little while before I can do anything, even rent a device to check compression. After my trip to Ft Knox last week my bank account is negative.

The worst fouling is when the valve guides start to leak and oil drains down onto the plugs.