78' 85hp OMC - Cuts out at Speed??

[Windsurfer]

I have a 78 85hp Evinrude that idles fine but when I go to plane the boat off and give it 3/4 throttle it planes off ok but then about 10-20 seconds later it cuts out to about half power. It barley planes the boat off. If I back it off and idle for a while and then plane it off again it will do the same thing. To me it sounds like a fuel problem. I checked the fuel filter on the side of the fuel pump and there was some jelly like stuff in there. Thought I solved it but same thing. I tried a different fuel tank and same problem. I pulled the fuel pump and dissambled it and it looked clean inside. Back washed the main and secondary jets with some compressed air. Checked if the flowed fuel freely and the all seemed good. Checked the compression, all about 130 psi. New plugs. Anyone have any sujestions before I pull the carburators off to see if I can find anything. also anyone know the correct gap setting for the spark plugs and the how much compression it should have?? I set the gap to .35 Any help is appreciated. Thanks

 

[JB]

Re: 78' 85hp OMC - Cuts out at Speed??

Hey, Windsurfer. Compression sounds excellent. Spark plugs: some books say .030, others say .040. you are probably in safe territory.<br /><br />Your engine behaves like it is starving for fuel. You recognize that and have checked it out. . . .except the primer bulb and the fuel tank venting and pickup. What happens if you pump the bulb when she is misbehaving?<br /><br />What else? Heat. When was the impeller last replaced? Do you have a strong, warm telltale?<br /><br />Long shots? Losing a cylinder or two intermittently. While it is in it's bad behavior, disable the plugs, one at a time. If killing a cylinder makes no difference, dead cylinder.<br /><br />That's enough (too much?) for one post. Let us know what happens.<br /><br />Red sky. . . . <br />JB

 

[Windsurfer]

Re: 78' 85hp OMC - Cuts out at Speed??

JB Thanks for the ideas, I already tried pumping the primer bulb when it was running to see if I could pump up the carberator and to see if there was still fuel in it. No luck, bulb was full of fuel and pumping did not help clear it up. as far as it gettime hot, if anything it's running cold. I belive the thermostats are stuck open because the block never realy warms up that much, I know that that could cause problems if it's running cold but usualy that affects idle speed more then anything else and it's idleing good. As far as pulling a plug and running it to pin point a trouble cylnder, the only oncern i have is what happens to the coil if it has no place to ground?? The high voltage is gonna try and find a ground somehow, just don't know what it's gonna do to get it. I suppose I could put an old plug in the wire and tie it to the block somhow to give it a path to ground. Thanks for the insight, I guess I'm gonna have to just keep trying things till i figure it out.