maybe a bad injector? or carb leaking thru.

 

I would have to see the plug to read it could be carbon build up, bad piston rings,,what kind of fouling is it ..oil ,ash,???

here is a chart

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

 

Cheap enough to change if you buy NGK from an auto parts store. They are less than 1/3 the price. I never use Champion plugs in anything Just my opinion.

 

Fouling on a four stroke engine is normally a fuel issue. Too rich. The question is why.

And do buy "marine" plugs. Use the plugs the manufacturer tells you to.

 

I had a similar problem with my 90 2 stroke. Carburators had to be rebuilt.
Ethanol is causing some major problems with outboards. Motor wouldnt idle
but run like a scalded dog on the high end. Kept fouling out the bottom cylinder.

 

Kagee is right on the too rich and fuel issue on a 4 stroke and is usually because of a stuck open thermostat or one that is too cold not allowing the motor to run at higher temps. When this happens the temp sensor tells the computer to richen the fuel mixture because it is cold kind of like a choke. Of course could be a bad temps sensor too but more often than not the thermostat.

When a bottom cylinder is fouling I would suspect a bad coil due to water hitting it when you set your boat down and lake water intrudes the cowling. A bad coil on most outboards will only effect about 500 rpms on top end rpms in most cases and also cause a slight rough idle.

 

I had the boat looked at after it refused to start and I flooded the motor. The mech synced the 4 carbs and it starts right up but kept the old plugs in that got drenched with gas. I then had the small miss at low RPMs. I just put in 4 new plugs NGKs. My question was how does the gas flooding the plug ruin the plug. To me if the plugs was good before I flooded the motor why doesn't the gas just burn off and the plugs still be OK. When I removed the plugs they all looked a little dark but the bottom was the worst.

Thanks for all the answers.

 

Fouling itself does not ruin the plugs. A fouled plug can be cleaned and re-used unless the plug itself is defective. Wet fouled or carbon fouled prevents the spark from arching at the anode. Sometimes they will clean themselves, most often not. Mechanics will just replace them because they don't want to mess with it.

Brake cleaner spray from the auto parts store does an excellent job along with a stiff bristled brush.

 

They can also be bead blasted at some mechanic shops.

 

My Honda would go through a set of Auto Lite plugs every season...Would just run like hell...Switched to NGK and havent looked back...it runs like a champ

 

I wood like to thank everyone for their answers. They have been very helpful.