5.0 mercruiser limp back to dock at 1500 rpm

[maddog2112]

Well my trusty 5.0 carbureted merc finally let me down. I had been trying to pin point an intermittent stumble while cruising issue and had decided it was a carburetor issue. Possibly a lean sneeze. Other than the occasional stumble she ran fine on the muffs and on the water. I decided to get her out today and live with the occasional stumble until rebuilding carb. Was running fine and then the stumble. This time she wanted to shutoff. I jockeyed the throttle and was able to keep her running but only at 1500 rpm steady. Anymore or less and she wanted to die. She got us back to the dock. I put her in neutral and jockeyed the throttle. Nice and smooth. No issues. But, when prop engaged, back to wanting to die when moving throttle. I was able to limp her onto the trailer and bring her home. Now I`m leaning against a carb issue as he runs fine with prop disengaged. Suggestions?? Thx in advance.

 

[Bondo]

Now I`m leaning against a carb issue as he runs fine with prop disengaged. Suggestions??

Ayuh,..... Actually, that symptom says fuel delivery,......

No Load means literally, Nothing,.....

 

[maddog2112]

So your still thinking carburetor?

 

[Grub54891]

Carb, fuel pump, or clogged filter/pickup in the tank...…

 

[QBhoy]

9/10 times this will be a delivery thing. First place to start is the pick up in the tank.

 

[maddog2112]

Thanks for the responses

 

[proby]

Is the boat overheating? Had a similar problem and it ended up being the impeller housing leaking.

 

[maddog2112]

Proby, no overheating. All indications normal.

 

[maddog2112]

suggestions for replacement electric fuel pump

Gonna start ripping and tearing on a fuel delivery issue. Just wondering where the best place and brand for replacement electric fuel pump is should I need one. Any experiences / suggestions ?

 

[Lou C]

First...
check the anti siphon valve on the gas tank for corrosion or debris...that can result in an engine that dies under load but runs fine with no load
check the tank vent
dump out the contents of the fuel filter in a mason jar and let it sit...do you see a layer of water or debris on the bottom?

after that...before replacing the electic fuel pump I'd test the pressure and volume...
if that's OK....
move on to the idle system of the carb...it sounds like its dirty, gummed up or the float might be sticking...

start with fuel delivery as noted then move on to individual components.

 

[wahlejim]

Isolate the problem. Run on a remote tank. If the problem persists, it is engine related. If it runs on a remote tank without issue, the problem is fuel tank/pickup related.

 

[maddog2112]

Thanks for the responses. I guess I skipped a few easier steps so far but I replaced my electric fuel pump with an OEM unit. Took her to the lake today and she ran smooth and strong. I thought I had nailed it but after a steady 10 minute run at 30 mph, a quick split second stagger. For a split second it drops 1000 rpm and then back to normal. This was my original problem . She ran perfect for another 10 minutes at a steady 35mph. Same thing. Just a quick split second stagger then back to normal. I did blow out my tank vent with air and it is clear. I will check for water in the water seperator next and then on to a carb rebuild if no water found. She`s run perfect for 10 years with all preventative maintenance applied . I guess it`s my turn to go nuts with this issue until solved. I just hope sharing this detail will help the next guy once I figure this thing out. Thanks for all the help .

 

[maddog2112]

One more tidbit of info. When I replaced my electric fuel pump, my carburetor inlet filter was extremely clean and the fuel line to fuel pump was clean and clear. Also, I blew out my tank vent line. I`ve heard people talk about the pickup tube but Have also seen where it`s almost impossible to remove without screwing the fitting up or worse. Has anyone ever blown air theu the hose thru the pickup to clear it ?