one plug fowling

My oil injected 2001 Merc 40 hp is running rough. I pulled both plugs (installed new this past Spring) and the top plug is pretty carbed up but the bottom one is clean. Is there an adjustment I need to make? FYI, I live on a river and mostly run at low RPMs, about 1400 to 2000.

Re: one plug fowling

I am having the exact same problem.
I too, run a river at low to moderate speeds.
The top plug is fouling and the bottom is clean as a whistle.
I have an 18hp Merc 2-stroke guesstimated 1994.

Re: one plug fowling

monstertruck said:

I am having the exact same problem.
I too, run a river at low to moderate speeds.
The top plug is fouling and the bottom is clean as a whistle.
I have an 18hp Merc 2-stroke guesstimated 1994.

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Monster,

Since posting I have read several posts related to this subject here (I'm sure some of the seasoned vets on this board are saying, quite rightly, that I should have done that first!). The first thing I'm going to do is a vigorous decarb. Do a search (seasoned vets: "There 'ya go!") for "decarb" and you'll find some good information. From what I've read, it is entirely possible that one cylinder has lost compression or has other ills due to carbon build up.

Also, many recommend widening the spark gap to .035 or .040 for low speed running. One post indicated that NKG plugs and higher quality oil in the mix can make a difference in some engines. I'll try these after the decarb.

I'll report back here with my results. Won't be until this weekend (8-22/23) though.

toon-e