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88 30 hp Evenrude problem once engine warmed up

M

martman

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" I've been chasing this p

" I've been chasing this problem for a few months now. What happens is when running at 3/4 throttle, after running 1/2 mile or so, the rpm drops to almost nothing then back to 3/4 throttle, then nothing, back up to 3/4 throttle, then shuts down. I can restart without touching the primer bulb. I can run all day at 1/2 throttle. I've removed thermostat, changed water pump, put new gasket under power head (bolts were loose and other gasket missing in places thinking exhaust was entering carb), and rebuilt carb. I've checked fuel screen on engine, changed gas, tanks and hose. This condition is minimized with the top off the engine, but I can feel the engine trying to shut down. I don't think it is a fuel problem but am running out of ideas. Does it sound like a power pack/ignition problem? "
 
"Martman.... If what you'r

"Martman.... If what you're speaking of is a slow surge of the rpms up and down, I'd suspect either a "O" Ring leakage problem at a plug on fuel connecter..... a fuel leak somewhere at any rate which would allow the fuel pump to draw air.

Another cause could be, if you're using a built in fuel tank, a sticking fuel anti siphon valve, as follows.

Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

Joe
"
 
" Joe,
Thanks for the reply.

" Joe,
Thanks for the reply. I'm speaking of running around 4200 rpm and it dropping down to 500 rpm, then back to 4200 down to 500, up to 4200 then shut down. I have a tiller handle and don't move my wrist or anything. I have portable tanks and have tried 2 of my tanks as well as 2 of a friends. Same outcome. The amount of time of the surge is approximately 1 sec per cycle.

I'll look for a leak at the plug on the fuel connector.

Marty "
 
" Joe,
No luck finding any fu

" Joe,
No luck finding any fuel leaks. I'm going to try the power pack off of a 25 hp I have access too. "
 
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