HELP: 2005 Mercury 115, 4 stroke missing at high rpm

[mbuhler]

I recently purchased a 24 ft triple pontoon with a 2005 Mercury 115, 4-stroke. The first few times I took it out on the water, it ran great. Max speed was about 27 mph, can't remember exactly, but over 5000 rpms. Now I am only able to go max 20 mph at about 4500 rpm and it begins to miss. The problem seems to be getting worse. I changed the fuel filter, but that is all I have done. Does anyone have any suggestions for what may be causing the missing at higher rpms? (It does not begin to miss until it is about 4500 rpm's).

 

[raymor]

Re: HELP: 2005 Mercury 115, 4 stroke missing at high rpm

When you say you changed the fuel filter was this an external or the one on the motor. I was told not to run my 115 hp 4-stroke without an external 10 micron fuel filter. I use the Yamaha one and change it every season. I have the same year motor as you do and the power head is made by Yamaha.

 

[pk_bob]

Re: HELP: 2005 Mercury 115, 4 stroke missing at high rpm

I too had a 4 stroke with the same problems on a crest 25 toon boat. Two trips to the repair shop, two sets of injectors and filters NO RESULTS. Just $1600 down the drain.

This past weekend, I was able to solve the problem myself.

1st I replaced the in line fuel filter, the old one has some black gunk in it.

2nd I added a fuel water/gas separator as external filter.

3rd When I cut the fuel line for the water/gas separator, the fuel line was goo inside the outer shell. That was the black stuff in the inline fuel filter.

4th I replaced the fuel line from the tank..bulb..w/g separator..to inline filter.

5th I removed the injectors and used carb cleaner to spray out the crap stuck in them. I also uses my compressor with pint point air stream to blow injectors from the pin hole side. Lots of junk came out.

6th I re installed the injectors.

7th The engine fired up with a whole new life and attitude. Our test drive got us to a sustained 5400 rpm with power and 30+ mph on the old girl. She's back to her old self.

Hope this helps.