Fuel Pump Issue (Urgent help!)

BarryCF said:

I may have missed the starting with wide open throttle, a classic way to clear a flooded engine. It runs rough for a few moments because of the raw gas present. It would help if we knew how, from where, the gas outside is coming from. That should never happen with a boat engine, any gas delivery issue should just dump down the carb. Is your fuel pump mechanical or electrical? Also, if you wait until the engine is cold does it start normally?

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I am not certain where the gas is coming from. I am thinking it could be that yellow/clearish over flow tube that people refer to?

I am not sure what the fuel pump is to be honest... I think it's original...

The engine starts normally when it is cold.

Cold starts OK, and hot starts are bad, and wide open throttle hot starts seem to clear it up. My best guess in this case, the needle valve operated by the float is leaking badly when hot, or the float gets stuck. Either will allow extra gas to flood the engine.

muskokamarc said:

I am not certain where the gas is coming from. I am thinking it could be that yellow/clearish over flow tube that people refer to?

I am not sure what the fuel pump is to be honest... I think it's original...

The engine starts normally when it is cold.

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If you have the yellowish /clear tube, that signifies a mechanical fuel pump is used. That tube flows fuel if the pump diaphram leaks. On a car fuel pump, that tube isn't present and just dumps on the ground through a weep hole (where marine tube connects).

If you have fuel in that tube, time for a new pump ASAP.

Fuel sitting on the manifold could also indicate that the shaft bushings on the carb shafts are worn out and fuel wicks along the shaft onto the manifold. Not that uncommon, just often missed. Marine carbs have different bushings than automotive ones, to prevent the wicking.

So the marina wants me to go by and basically demonstrate the problem. Problem is I don't know how the heck to recreate it! Loves to happen on a hot day when i drive for 30-40 minutes and then stop for lunch... I guess I'll need to do this? Or is there another way to recreate this problem in a shorter time?

Bill Curtis said:

If you have the yellowish /clear tube, that signifies a mechanical fuel pump is used. That tube flows fuel if the pump diaphram leaks. On a car fuel pump, that tube isn't present and just dumps on the ground through a weep hole (where marine tube connects).

If you have fuel in that tube, time for a new pump ASAP.

Fuel sitting on the manifold could also indicate that the shaft bushings on the carb shafts are worn out and fuel wicks along the shaft onto the manifold. Not that uncommon, just often missed. Marine carbs have different bushings than automotive ones, to prevent the wicking.

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Good point on the pump tube. I had forgotten there is a tube to remove the fuel from the pump in the event of a busted diaphragm. That might be the culprit. Should be easy to see as there should be no fuel at all. It would certainly flood the engine. It doesn't explain why it starts OK cold though, unless the diaphragm leaks when it gets hot. That's certainly possible.

UPDATE - These are the notes from the mechanic at the marina

“Remove top of carb and check float level - correct. Install new float as a means of correcting a possible failure. Run engine - after a period of time the carb floods and continues to overfill. After engine stalls, the fuel keeps running until the supply of fuel in the line from the water sep filter to the carb is spent. Check anti-syphon valve at fuel tank - intact and operating properly. From an identical engine removed from a customers repower job, swap out carbs and run engine. The exact problem re-occured. Connect vacuum and pressure test gauges to the mechanical fuel pump output side and run engine. Pump pressure gradually climbs from the normal 7 psi to 16 psi and holds steady, until the engine dies from flooding. Pump operating specs are 5.5 to 6.5 psi @ 1100 rpm. Swap out mechanical fuel pumps from other engine, connect test gauges and run engine. Pump pressure steady at 6 psi and less than 1" Hg for vacuum. Remove test equipment and water test. Water tested well. The ignition amplifier is NLA as is a replacement timing chain. Everything now left in a state that the customer can get the boat and drive it to see if he is satisfied.”

Does this mean its the fuel pump!?

"Swap out mechanical fuel pumps from other engine, connect test gauges and run engine. Pump pressure steady at 6 psi and less than 1" Hg for vacuum"

Sure seems like it to me

Shaps said:

"Swap out mechanical fuel pumps from other engine, connect test gauges and run engine. Pump pressure steady at 6 psi and less than 1" Hg for vacuum"

Sure seems like it to me

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Very glad they were able to find that issue and i hope that is the end of it...

I started searching about the ignition amplifier and noticed that it could also be a culprit if it gets too hot?

muskokamarc said:

Very glad they were able to find that issue and i hope that is the end of it...

I started searching about the ignition amplifier and noticed that it could also be a culprit if it gets too hot?

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Sounds like the problem is solved and the fuel pump was it. Great to hear it. Too much pressure will push gas by the needle valve.

Any overheated electronic part can fail, but the ignition failure would not cause flooding. If I'm not mistaken your engine is a 350 Chevy base, so I would think there is not a shortage of marine ignition replacements available and the same for the timing chain. Maybe there is something I'm not aware of.

FLOAT IN CARB HAS HOLE IN IT. SO AFTER IT RUNS ON COLD START THE FLOAT FILLS UP. CARB THINKS BOWL IS EMPTY SO IT DUMPS MORE FUEL IN

km1125 said:

There are only two things that would cause fuel to get outside the carb... either the fuel pump is putting out too much pressure (which is VERY rare, but does happen), or the carb has a problem either with leaks or the float mechanism.

It's an easy test to check the pressure out of the fuel pump and unless that shows an issue, this is a CARB problem. Whoever rebuilt that probably didn't do a good job, but I wouldn't be surprised if that's the case, especially after reading that paragraph of "diagnosis and recommendations" listed earlier. I'd also suspect their compression measurements and want to have that test redone by someone competent to verify those numbers.

Holley carbs are great, but they have their foibles just like Rochesters. A good rebuilt Rochester would be fine on that engine as would a new replacement. A new replacement shouldn't cost anywhere near $1500 but less than 1/3 of that.

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You were pretty much right with respect to the fuel pump being the problem!