4.3 mercruiser once warm, fuel starvation

[samm835]

I have a 97 4.3 mercruiser lx. The motor runs well, but will stall after driving for a 10/15 minute ride. It will start back up, but then stalls again after another couple of minutes. It not over heating, I've changed the fuel separator, so I am looking for things to start trouble shooting. Thanks

 

[SeaDooSam]

Did you check the carb for dirt?

 

[samm835]

I haven't checked the carb yet, I'm by no means a mechanic, but know enough (can get me in trouble), whats the best way to check carb for dirt?

 

[Rick Stephens]

Something like this can be the anti-syphon valve on the fuel tank end of your fuel line getting plugged up with crud.

Could be a plugged up breather for the fuel tank. If you open the fuel filler cap does it gulp air?

It can be a dirty carb - which means getting a rebuild kit and taking apart and cleaning it. While not hard, rebuilding a carb is one of those things that seem to fairly often get done wrong and need doing over again. It takes finicky attention to detail, which seems some people aren't inclined towards.

First few things come to my mind....

 

[samm835]

Thanks for the things to think about, I was thinking about the siphon/breather tube, I dbl ck today. I was thinking also, will a fuel pump intermittent work?

 

[Rick Stephens]

Not likely that a fuel pump changes behavior. Electric or mechanical? Most likely fine but you can pull the line off the carb and stick it in a plastic soda bottle and crank your engine, see if it is pumping well.

 

[samm835]

That was what I was thinking as well, its electric but thought I would verify. The odd thing is, that this will do same symptoms each time out. Ride great, then 15mins acts as if fuel starved, shuts off, pump fuel then starts again, but at this point shuts off every minute of ride

 

[Rick Stephens]

With your electric, if push comes to shove, you can install an inline fuel pressure gauge and see what it is doing. Too expensive to just drop a new pump in there.

 

[samm835]

So I went out to the boat last night, the carb looks fine. The fuel pump sounds as if its working (hum), I forgot to bring a volt tester....so I'm still stumped. Should be looking at a coil that might be bad once it gets warm?

 

[krakatoa]

Something like this can be the anti-syphon valve on the fuel tank end of your fuel line getting plugged up with crud.

I will go with this one. This valve have a spring and a like a bearing that sometimes get stuck and doesnt allow the gas pass to the carb. Happen to me once. I would love get rid of that bearing inside the valve.....

 

[samm835]

Where is the anti-syphon valve located? Quick check and fix?

 

[Bondo]

Where is the anti-syphon valve located? Quick check and fix?

Ayuh,.... It's the hose barb fittin' at the tank's outlet,....

 

[krakatoa]

Grab a carburetor cleaner bottle and spray directly into carb while the engine is on, spray on a couple of time while some buddy just hit the choke. My boat had same trouble since it was siting over 4 years as far as I know. I did the anti-siphone valve and yes, it was clugged, I change then the fuel line, watrer fuel separator and replace the anti-siphone valve with a brass valve with no bearing and spring. Now the engine is running fine with no starvation but Im still on muff. Needs to launching and hit the throttle so the carb spit out remaining "dirt" or gump.

Would like to know how your troubleshooting ends and what you did up to date.

here is how the setup looks (pic was before the parts update)