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5.7 litre V8 Mercury Mercruiser.

G

Geoff Barwick

New member
<p>
5.7 litre V8 Mercury Mercruiser. Caburetor. Manufactured Dec 2006. In a ski boat. Engine and boat ran fine for three hours. Then suddenly stopped when under power. Will start up instantly again. Will idle and can even rev up when not under load. But engage drive and can idle about but cant rev up. If rev up under load it will pic up revs for a second or so and then engine cuts out. Will immediately start again. Engine idles under load just good enough to get back to the boat ramp and go home. Ive done all the obvious stuff. There is no blockage in the air vent line to the fuel tank. I even undid the fuel cap to make sure air getting in. Ive changed the fuel filter. There was no water or crud in the old filter anyway. Ive pulled the carbi apart thinking there would be some blocked jets. The carbi was clean and nothing wrong with it. Drained old fuel and put new high octain fuel in. What is next step? Getting to the limits of my mechanical abilities.</p>
 
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How about the anti-siphon valve on the fuel tank? This is a spring loaded valve that shuts off fuel flow if the fuel hose from the tank to the fuel pump leaks. For fuel to flow the fuel pump must be able to pull the internal ball off the seat and compress the spring inside. When the engine is shut off the spring closes the fuel flow. If the valve is clogged with crud from the tank or the ball inside is corroded it will stick and limit fuel flow. You can try running the engine on an outboard fuel tank to test. I had this same problem when I bought my 1988 Four Winns back in 2002. I did everything I knew to do but I didn't know about the anti-siphon valve. My mechanic tested it and replaced it with a better quality valve back in 2004 and no problems with that ever since.</p>
 
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I'd suggest a bit more effort in the troubleshooting department before you continue ... you need to determine if the cutout is due to fuel or lack of spark...and I'd be inclined to think the latter based on the "will start up instantly" observation...a timing light can be a geat tool in these circumstances...
 
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