25 hp Evinrude hesitates at WOT

[psully]

4-23-08
I have a 25hp 1994 Evinrude mounted on a 1994 16 1/2 ft. Northwoods
aluminum deep v fishing boat. The motor starts great and idles well but will hesitate when cold or warm . The hesitation seems to last for several seconds and then it will take off full throttle again for few minute then repeat the problem. The motor never shuts off, it just hesitates/stalling but never shutting off. I have tried shutting it off and starting it again and it starts great. Sometimes the problem disappears for hours, and also it may be coincidence but if I wiggle the gas line hose it sometimes seems to help. I checked the engine gas filter and it's clear. Any suggestions or tests I can do to diagnose the problem?

 

[Dennise]

Re: 25 hp Evinrude hesitates at WOT

- air leaking into fuel line
- restriction in fuel line
- fuel tank not vented
- water in fuel
- old fuel
- bad fuel/oil mixture fouling plugs
- fouled plugs
- bad thermostat

 

[psully]

Re: 25 hp Evinrude hesitates at WOT

Dennise,
Thanks much for the fast response and checklist,I think I'm going to start by replacing the fuel tank/hose and work my way down your list. I don't see a vent on the gas tank, is it supposed to be self venting? The new fuel tank I bought has a vent screw on top but no instructions should I open the vent screw slightly? Isn't the tank,fuel line hose supposed to be pressurized?