20hp Mercury

Question
I have a 20 hp Mercury manual start outboard motor mounted on a 14ft Duracraft aluminum boat. Model and year are unknown. I would assume it is an 80's model. It continuously fouls spark plugs. The symptoms while running are; if going full throttle it will suddenly kick down to just above idle speed, this is unpredictable, after running that way for a while it will unexpectedly kick back wide open which scares me to death each time. Any advice or opinion would be greatly appreciated

Answer
Hi Byron...thank you for selecting the undersigned to respond to your question. Bear in mind, I'm not a mechanic.

The symptoms suggest a fuel restriction of some sort, and perhaps the diaphram is defective, or their might be a problem with the fuel pump. When you check the spark plugs for fouling, are they damp or wet? That indicates too much fuel. If they're black with carbon, you're not getting full ignition. Have you checked all fuel line connections to ensure they are secure and haven't loosened off?

If all else fails, best you consult a qualified and reliable marine mechanic to assist you to resolve the difficulty.

Safe Boating
Ron