For discussion, mercruiser v6 , rochester, edelbrock

[Bt Doctur]

This is my personal boat and have been working on it for about 2 years. 4.3 ,mechanical fuel pump, rochester 4 bbl. Needed to do a haul so I needed to get off my trailer. Motor would not idle so I did a quick and dirty quick cleaning and had a stable idle. Put the boat in the slip , did the haul and took it out for a test. Good 2 barrel performance but starving with the throttle opened up. The second run did good at the higher speeds but carb was flooding out at idle. Stumbling, black exaust, etc.Expected as much for sitting 2 years.

Replace it with an edelbrock that was new and had been borrowed for a week until the customers carb came back. No issues at all on my customers motor.

Put it on my motor and when cold runs and idles perfect. When hot runs good at above idle but will flood at idle. Mechanical pumps are not supposed to increase fuel pressure
but this has one stumped. Was going to test with an electric pump but the weather closed in on me .

Any thoughts?

 

[Lou C]

check fuel pressure?
that sounds like on both carbs the needle valve might be overwhelmed by too much fuel pressure. However, its a problem I've never had with both the original pump (Carter) and the Sierra I replaced it with 2 years ago. Is the pump original or has it been replaced?
How about debris in the fuel, or deteriorating fuel line causing the float to stick?
take sample of fuel from the water separating filter and see what is on the bottom, debris, water?

 

[alldodge]

I also think good possibility of fuel pump pressure is a tad to high

 

[Bt Doctur]

pump has not been changed, filter shows nothing. I can understand the rochester being dirty inside but not the edelbrock.
I`ll post an update in the spring. This is the same pump that was on the motor when the OP owned it and same carb. Never an issue.

 

[Rick Stephens]

Anyone one else I'd suggest a plugged up flash arrestor.

 

[nola mike]

I also think good possibility of fuel pump pressure is a tad to high

What would make the pressure all of a sudden jump on a mechanical pump? I'd still think of carp in the needle seat, would clean it out and run it in a remote tank to check.

 

[Lou C]

If it happens with 2 different carbs then it’s something that would affect both; I guess then besides the fuel pump, maybe a bad load of gas, deteriorated fuel line etc

 

[Scott Danforth]

water in the fuel tank or dirty spark arrestor.

 

[vroom ZOOM]

Well... Yes, there is a possibility of fuel pump pressure jumping up. The average pressure doesn't jump up, it something else. There is a little diaphragm in the fuel pump, downstream from the main pumping diaphragm. This little diaphragm has the fuel on one side, and a sealed air pocket that acts like a spring on the other. When the fuel comes from the pumping diaphragm, it comes in short hard spurts, sort of like closing a bathroom tap really quick and hearing the pipes shake. So the little diaphragm, called a pulsation damper, prevents these hard spurts from upsetting the needle. If it gets a hole in it... then the fuel pump spurts slam the needle down and flood the carb. In other words, the peak pressure that the pump is producing goes up. So yes, a mechanical pump can flood a carb when it goes bad, and yes, this has happened to me. I rebuilt my carb, but it was still flooding. Chances are you need a new pump.

Another STUPID hint: Not sure if the carter pumps come with these, but there is often a spacer between the pump and block, this makes the pump stroke shorter and reduces the fuel pressure, maybe it fell out and you didn't notice?

just my 2 cents