1989 OMC 5.7l Chevy Engine stalls under load.

Boat is a Four Winns Liberator 201 running an OMC 5.7l V8 with 4 barrel Rochester carb. Engine is based on the Chevy lump.

Runs fine at low and no load but when powering up to 50% plus of WOT engine starts to cough and will stall if the throttle is not reduced.

Will rev freely to WOT when out of gear.

We're investigating based on some sort of fuel flow / restriction issue and so far have the following thoughts:

Fouled fuel (water etc.). Seems unlikely as this thing drinks the old unleaded so it's never really in the boat long enough to become fouled. Also seems unlikely that duff fuel would give such a predictable problem?

Blocked carb jet - the current favourite theory. It's effectively a 2 stage carb, 1 set of butterflies open at low rpm and second set at some point later. This will be investigated with a carb strip down and clean.

Can anyone offer any other likely avenues of investigation?

Re: 1989 OMC 5.7l Chevy Engine stalls under load.

Fouled fuel (water etc.). Seems unlikely as this thing drinks the old unleaded so it's never really in the boat long enough to become fouled. Also seems unlikely that duff fuel would give such a predictable problem?

Blocked carb jet - the current favourite theory. It's effectively a 2 stage carb, 1 set of butterflies open at low rpm and second set at some point later. This will be investigated with a carb strip down and clean.

Click to expand...

Ayuh,... Sure does sound like a lean fuel condition,....

What's the contents of the fuel Filters look like,..??
And the inside of the carb,..??

Re: 1989 OMC 5.7l Chevy Engine stalls under load.

When I bought the boat in April the marine engineer i bought it from had recently restored it and it ran perfectly, while I had the original distributor and points. However, I also took his advice and installed the after market ChevPro marine electronic distributor and associated ESA. I did have some issues as the supplied ESA was incompatible with the new dizzy, however those issues have been resolved now.

Coincidentally this problem occured when I used the boat for its longest period under my ownership. Initially it coughed when I powered up after it had covered about 10 miles so I backed off and gently cruised for 5 miles where the family disembarked. I then went to return home and on powering up out the estuary speed control area the engine stalled. It restarted but failed successively with fewer revs and a smaller time duration between failures until it would go no more and the RNLI recovered me.

This weekend I shall winterize the boat and remove the sterndrive to replace a split bellow. I shall also remove the carb and fuel filters and give these a visual inspection. It'll also give me the part numbers I need to order the correct filters etc. Is there any way I can check the fuel pump diaphram hasn't split as I suppose this could be a suspect?

Re: 1989 OMC 5.7l Chevy Engine stalls under load.

When I bought the boat in April the marine engineer i bought it from had recently restored it and it ran perfectly, while I had the original distributor and points. However, I also took his advice and installed the after market ChevPro marine electronic distributor and associated ESA. I did have some issues as the supplied ESA was incompatible with the new dizzy, however those issues have been resolved now.

Coincidentally this problem occured when I used the boat for its longest period under my ownership. Initially it coughed when I powered up after it had covered about 10 miles so I backed off and gently cruised for 5 miles where the family disembarked. I then went to return home and on powering up out the estuary speed control area the engine stalled. It restarted but failed successively with fewer revs and a smaller time duration between failures until it would go no more and the RNLI recovered me.

This weekend I shall winterize the boat and remove the sterndrive to replace a split bellow. I shall also remove the carb and fuel filters and give these a visual inspection. It'll also give me the part numbers I need to order the correct filters etc. Is there any way I can check the fuel pump diaphram hasn't split as I suppose this could be a suspect?