OMC 5.7l V8 Problem

[paddy01]

Hi,

Posting on behalf of a friend who's got a problem with his power plant.

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?

Cheers!

Paddy

 

[paddy01]

Just thought, this might be more proper in PBO Reader to Reader. If so please could a mod move.

Thanks.

 

[moonraker 36]

their are some knowledgable people on here..
but if you dont get any joy try the iboats forum.

you can get good info on stripping and rebuilding the quad/carb on youtube...

 

[paul5150uk]

have you change the fuel filter

would do that 1st before looking at the carb

had same problem on my 5.7l omc few years ago ran fine low revs open her up and would stall and splutter was fuel filter

 

[paddy01]

Thanks for the suggestion moonraker, I believe he is a member on iboats and will be posting there.

paul - thanks for the suggestion, certainly a candidate, we'll try that. As far as I can see there's a single inline filter so should be a simple test.

Cheers

Paddy

 

[Assassin]

Also chech the air supply, and check the coils are not breaking down under load, this is fairly common.

 

[moonraker 36]

theirs a small fuel filter in the carb its self.you just disconnect fuel line to get o it.

 

[Jurgen]

Just had the same problem with my engine, again a 5.7 ltr v8 with Holley carb.

Have rebuilt due to leaking accelerator pump gasket but while at it discovered the real problem was the secondary butterflies were not opening.

After a bit of a heath robinson fix i managed to secure the throttle linkage bar to the secondary butterlies with a bent paper clip, I KID YOU NOT LOL.

Will refit the carbs at the weekend and report back.

 

[paddy01]

Thanks all for the info. Very useful and shall be passed right along.

I've got a gentleman's wager on fuel filter