Mercruiser GM350 V8 Dies quickly after starting

[georgeiv11]

Hi All,

First forum post ever, hopefully I follow the rules.

I have a 1995 Wellcraft Runabout Sterndrive with a Mercruiser/Chevy V8 350, carburetor, Mechanical fuel pump.

I've used the boat about 7 times this year and it has run flawlessly. I started it on muffs last night and it ran for about 1.5 minutes then died (with a little throttle applied out of gear). Then consecutively ran less and less, because it's run so well this season I'd be surprised if it was a carb issue. I ran it two weeks ago for about 3 hours, started nicely each time and ran well.

The boat does have fuel it in, new plugs last year and new distributor cap. I'm trying to diagnose/go down the right path in diagnosing the issue.

What I think so far is that it is a fuel issue, but would be surprised if it's the fuel pump. The fuel filter is filled with fuel. The ignition lanyard does make the siren sound when the key is in the on position so I don't believe it's the front end for the kill switch but it could possibly be the backend?

What steps/order of steps should I be taking? The boat seems to run if I prime the engine as well, and then dies off.

Thank you all in advance... have a few people counting on me over the 4th so hoping it's fixable.

 

[81 Checkmate]

Take the fuel line off the carb and turn it over with the coil wire off and see if you getting fuel. If not then its the fuel pump. Be careful not to get fuel on ignition parts. Hold the line over the carb.

 

[Rick Stephens]

Need three things to run: compression, fuel and spark.

I agree with pulling the fuel line off but I'd stick it in a plastic coke bottle and catch the fuel. Probably before I did that I would pull the flame arrestor off and have someone cycle the the throttle while I looked to see if any fuel squirted into the carb from the accelerator pump.

Second I would pull a plug wire and a plug, ground it and see if I have spark.

Rick

 

[81 Checkmate]

Just to note - on my recent rebuild we install a brand new OE fuel pump from amazon and worked for about an hour. And the same thing as you described happened. While never the less when moving the throttle it would squirt fuel in the carb, but when I disconnected the fuel line and turn the motor over it would spit a little fuel then none then a bigger spit and so on. It was getting fuel to the carb but not enough to keep it running. Install a new Sierra pump and all is good.

 

[georgeiv11]

I really appreciate the advice and replies, it ended up being the ignition lanyard. Turns out it was delivering intermittent power causing the engine to cut out... interesting.