470 Carb issues- Rochester 2bbl

79 Mercruiser 470 ? 2-barrel Rochester 2CG carb.
Engine is mechanically sound. Good consistent compression, new cap/rotor/plugs.
I rebuilt the carb a few months ago and it ran great- no problems at all. This was in the winter. Fast forward to now.

The boat runs excellent on the muffs in the driveway, starts right up, idles right away.
When I take it out on the water things go south. Last Sunday it started right up at the dock, idled out a few hundred yards and died- couldn?t start it back up. The only way it would stay running is if I pumped the throttle. The accelerator pump is working and I think that is the only reason it would stay running ? but just barely. It seems that when it gets over 125 degrees it doesn?t want to run any longer. I think I can rule out vapor lock because the accelerator pump is always working.
I can?t get the temp up much past 130 in the driveway since we have pretty cold well-water and I don?t have a way to put a load on it.

I think I am going to fabricate up a tub to put the outdrive in and get some kind of load on the engine to get it up to operating temp.

It seems obvious that I am not getting fuel but it is getting to the carb since accelerator pump always works
Do you guys have any suggestions what might be the problem with my 2CG?

Thanks,
Jake
Oakley, CA

Re: 470 Carb issues- Rochester 2bbl

check your fuel filters. sound like water in fuel.
as you trailer it your mixing the tanks up. so possibly waters getting in the tank. I had the same prob i just changed the filters and i was fine

Re: 470 Carb issues- Rochester 2bbl

Another thing to check is the vacuum operated spring loaded power piston in the center, under the air horn (carb cover) controlling the metering rods to the primary jets, make sure it is not frozen in it's bore but moves freely along with the spring pressure.

Re: 470 Carb issues- Rochester 2bbl

On land (trailer) the engine is at one level. On the water, it is different. The stern will squat prior to planing. Check / raise your float level in the carb. I did the same thing as you - rebuilt carb to spec and it ran fine on the trailer.

On the lake, I removed the top of the carb and saw the problem - the fuel level wasn't high enough. Adjusted the float setting and no problem since.

Re: 470 Carb issues- Rochester 2bbl

Sounds like some good things to check. I am going to drain the gas in case there is water in the fuel. How can I tell if there is/was water in the fuel once I get it out of my tank?

Thanks
jake

Re: 470 Carb issues- Rochester 2bbl

jakeb said:

Sounds like some good things to check. I am going to drain the gas in case there is water in the fuel. How can I tell if there is/was water in the fuel once I get it out of my tank?

Thanks
jake

Click to expand...

Your spin on filter is supposed to keep that from happening, it is a filter/water seperator. If you take off the top of the carb, you would see usually rusty water in there, if there is any?
How is your antisiphon valve working, & fuel screen at, & in the fuel tank?

Re: 470 Carb issues- Rochester 2bbl

I had a similar problem, but it was that I had two spark plug wires backwards. When it was running out of the water it ran smooth because there was no load. When it was in the water, it bogged down and died and had a hard time restarting.

We realized it when I had the boat running out of the water. We pulled a spark plug wire while it was running and no change. I pulled a second wire... it almost died so I put it back. I pulled the third wire... no change. 4th wire... almost died... put it back. As soon as I hovered the first wire over the 3rd the engine ran better. And I put the 3rd back on the 1st... ran smooth as a butta'. We put it in the water and vroom, vroom.

470 engine -- mmmm yeah. I guess I didn't understand the firing order stamped on the engine. :|