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Mercruiser 3.0 stalls when throttle opened

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Pawulu37

New member
After the winter this engine wouldn't idle, so I rebuilt the carburetor with an aftermarket kit. (Mercarb not Rochester) Now it starts right away and idles smoothly. But when running, it will stall with increased throttle. We can be going great at 50% throttle, and when I increase to 60% it just dies. I thought maybe the throttle cable was stiff and causing the ignition kill switch to kill the engine, but that seems fine. Now I'm wondering if the accelerator pump is not working properly. When taking off, from idle to 20% throttle it doesn't stall, but going from 50% to 60% or from 60% to 70% it stalls. If we very gradually open the throttle it is fine. Somewhere I read that the aftermarket accelerator pumps aren't as good as stock. Or is there something else that it could be?
 
Your description points to the accelerator pump.

It could be a few different things causing the pump not pushing fuel exactly at the same time as throttle shaft movement.

Possibly float level is wrong not allowing pump well to fill properly or pump umbreller not wiping well properly or you have accelerator link rod in wrong hole causing pump to depress to deep in well at 1/2 or more throttle.

Seeing as you rebuilt it this is where you should start.


The Accelerator pump/squirt MUST move and squirt exactly at the same time the main throttle moves. Pay very close attention to link rod and that its not bent wrong causing play before accelerator lever and pump move or hole in lever is worn/oval as it must be round.
 
kghost said:
Your description points to the accelerator pump.

It could be a few different things causing the pump not pushing fuel exactly at the same time as throttle shaft movement.

Possibly float level is wrong not allowing pump well to fill properly or pump umbreller not wiping well properly or you have accelerator link rod in wrong hole causing pump to depress to deep in well at 1/2 or more throttle.

Seeing as you rebuilt it this is where you should start.


The Accelerator pump/squirt MUST move and squirt exactly at the same time the main throttle moves. Pay very close attention to link rod and that its not bent wrong causing play before accelerator lever and pump move or hole in lever is worn/oval as it must be round.
Click to expand...

Hmm... You mentioned the float level, and I was careful to set that according to the specs. But you got me thinking. I wondered if the accelerator pump well was starved when the boat is pitched up (not planing), but the carb is oriented so that the accelerator pump is toward the rear, (should I say aft?) so it shouldn't be starved. Maybe flooded, if anything. The linkage seems to be okay. (the only way to adjust this one is by bending it, and it's not that easy.)

I pulled it apart again to see. I found the old accelerator pump piston, (which thankfully I didn't throw away) and the rubber seal is much stronger than the new one, which seems very thin and flimsy. So I put the old piston back in the carb. I couldn't see any other problems in the carb.

It was several weeks before we got a chance to put the boat back in the water and test it. I took it for run and it didn't stall at all. I couldn't tell if there was still some hesitation when I open the throttle, but at least it kept running! It seems to be better. It starts easily and idles smoothly, so I'm thankful for that.

Now we're putting it away for the winter, so we'll try again next season.
Thanks a lot for your help!
 
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