120 hp OMC fuel pump ?

[blinkie2843]

We recently aquired a 1984 Cobia Sportster, nice boat, powered by a 120hp OMC which is a 2.5L from what I can gather. But. We've had it out twice and both times it seems to starve for fuel about a mile from the dock. After the first time we drained and cleaned the fuel tank, replaced the fuel line and filter, really found nothing. We've cleaned and reset the points, has a new coil, plugs are good, valves reset. Last time out when it started to die I put a wet rag on the fuel pump and it seemed that as long as I did that it ran fine. So my question is, has there been a problem with vapor lock in the fuel system on these engines. Should note the first thing I tried was taking of the fuel cap in case it wasn't venting, that didn't help. also engine temp is good 175-180 F. When the engine starts to die you can hear it start to ping like possible lean condition. I'm a 30 year licensed truck/auto tech but am pretty green on marine stuff. All ideas appreciated.

Thanks, Bob

 

[Bondo]

Re: 120 hp OMC fuel pump ?

We recently aquired a 1984 Cobia Sportster, nice boat, powered by a 120hp OMC which is a 2.5L from what I can gather. But. We've had it out twice and both times it seems to starve for fuel about a mile from the dock. After the first time we drained and cleaned the fuel tank, replaced the fuel line and filter, really found nothing. We've cleaned and reset the points, has a new coil, plugs are good, valves reset. Last time out when it started to die I put a wet rag on the fuel pump and it seemed that as long as I did that it ran fine. So my question is, has there been a problem with vapor lock in the fuel system on these engines. Should note the first thing I tried was taking of the fuel cap in case it wasn't venting, that didn't help. also engine temp is good 175-180 F. When the engine starts to die you can hear it start to ping like possible lean condition. I'm a 30 year licensed truck/auto tech but am pretty green on marine stuff. All ideas appreciated.

Thanks, Bob

Ayuh,.... Welcome Aboard Bob,... It's runnin' a High temp, ya oughta put in a new impeller in the raw water pump,...

I'd Guess the fuel pump might be failin',...
Pressure test it,... oughta be 'bout 5 psi at the carb...

Did ya change the filter inside the pump,..?? how 'bout the 1 in the carb's inlet,..??

If ya really think it's vapor lockin',.... run it with the motorbox open or off...

 

[blinkie2843]

Re: 120 hp OMC fuel pump ?

Ayuh,.... Welcome Aboard Bob,... It's runnin' a High temp, ya oughta put in a new impeller in the raw water pump,...

I'd Guess the fuel pump might be failin',...
Pressure test it,... oughta be 'bout 5 psi at the carb...

Did ya change the filter inside the pump,..?? how 'bout the 1 in the carb's inlet,..??

If ya really think it's vapor lockin',.... run it with the motorbox open or off...

Thanks, sounds like you've seen this before and vapor lock is not know problem. Likely makes sense, this boat hasn't seen water in a couple of years and before it sat a marine place somewhere did a head on it,( so the story goes) gotta wonder why? We tried to be sure it had water flow before we put it in the river, seemed OK and the temp gauge seems to work 170-180 but I did think it seemed hot. Just had the rear unit off to replace the transom seal maybe we should have gotten more parts.

 

[blinkie2843]

Re: 120 hp OMC fuel pump ?

The rest of the story, removed and tested thermostate OK, so much silcone where the gasket was water intake 90% blocked, redid the gasket at exhaust conection, hoses from manifold to thermostate BACKWARDS, replaced raw water pump impeler and from what I've read the one in it was backwards? tested fuel pump volume and replaced, installed electronic ignition conversion kit. Runs like a champ now.