Engine Missing

[Hook1]

So recently I've noticed my motor running rough at high rpms. It runs perfect from startup to about 3/4 throttle. Once I get wide open for a short time it starts to cut out and the rpms go up and down. I replaced the plugs with no results and was thinking the next step would be the fuel filter. The fuel lines dont feel mushy and the bulb stays pretty firm. I dont really think the carb needs work since it starts easy and idles smooth. Any one ever had this problem? I just think its starving for gas at WOT. Its a Mercury 90 ELPTO 2 stroke if that matters.

 

[roty967]

Do you have a vent on the gas tank?? If so make sure it is open to allow fuel to flow and stop tank from collapsing if it is plastic. Simple ideas first...

 

[Hook1]

Yes it has a vented gas cap. I can press on the tank slightly and hear air pushing out.

 

[roty967]

Ok that should be vented enough then. I'm no expert but sounds like fuel issue to me.

 

[vhype]

Sounds like fuel filter.

 

[chillerman69]

I have a large canister filter on mine and the manual says to run it no more than 50 hours. I second or third the filter and hope that does the trick for you but since computers have been on any type of engine, an electrical and fuel issue are hard to tell apart. My next cheapest move, if you haven't been doing it, would be to run a 2 cycle fuel injector cleaner. If you seldom or never use it, you may need to shock it with a high dose. good luck and hope this issue is easy on the pocketbook

 

[wildturkey]

Could be the fuel line if you use ethanol added gas.

 

[Hook1]

wildturkey - 6/3/2014 5:34 AM

Could be the fuel line if you use ethanol added gas.

I've never used ethanol gas. I always bought it at HBSP or in Ft. Oglethorpe at the 100% gas place. I occasionally run a bottle of Berriman's B12 in it if I happen to top off the tank. I removed the cowl last night and none of the fuel lines feel soft enough to collapse which is what I've heard of before. The fuel filter looks like its gonna be a little bit tough to get out of there. There is a really short piece of hose on either end with a 90 deg. bend and some other stuff in front of it. Theres just not much room to even look around in these outboards.

 

[TheFisherman]

I know this is an old thread but here's the similar experience I had this year on my 2000 225 ProMax. Same thing, a little miss at higher RPM's. THought it could have been gas too, or water, but started with the spark plugs ecause am always careful to use 92 octane no ethenol gas and Stabil in the winter months. One plug had a bit of rust on the tip where the wire attaches. Not enough of the dielectric grease on it. I went ahead and put all new plugs and added thin coating of the dielectric grease. No more miss. Now one could argue that it just needed new plugs, but my theory is that the rust added just enough resistance at higher RPM's to cause a voltage drop on that particular plug to cause the miss. I could have just cleaned up the one plug to get rid of the rust and put it back in and solved the issue. Anyway, it's an easy thing to neglect when changing plugs. I don't know what the difference is between dielectric grease and petropleum jelly but my guess is that at least the dielectric grease is prolly petroleum jelly based. Since I've always coated battery terminals with a little petroleum jelly to facilitate a good connection that won't corrode, my suspicion is that they are simply one and the same. Someone that knows can correct me on that please, if I am wrong. BTW, my mechanic agreed that my theory was very possible and was likely the cause of my miss.