Intermittent Low Speed operation 2005 Merc 115hp 4-stroke

[cps22]

I have a 05 Merc 115hp 4-stroke that has a intermittent low speed problem, but seems to be getting worse.
At times while motoring along slow, maybe 2000 rpm the engine will begin to run rough. If I take it to 4000 for awhile then back off to 2000 again, it generally runs better for awhile.

I replace plugs, fuel filter, ran seafoam through 2 tanks. I checked the fuel rail pressure last year before putting the boat away and I recall that it was within spec, I think 65lbs pressure.

Again, at higher speeds, all is well.

Any suggestions welcome.


Thx

 

[raymor]

Re: Intermittent Low Speed operation 2005 Merc 115hp 4-stroke

Had the same problem with my 2005 115hp 4-stroke. I see you already replaced the spark plugs as that was my problem. It would break up
around 1800 rpm and clear up around 2200 rpms. Wonder if you have a weak coil? Put a timing light on it to find which plug is intermittent.