Desperately need help from the 40 Merc guys

[BRzuki]

The diaphragm on the front side of the pump that is actuated by the top cylinder via vacuum hose was breaking down (delaminating) thus flooding the top cylinder at WOT. Fixed that issue and it ran great. The jetting is just to get it leaned out to where I feel comfortable with it.

[Bill Van Steenwyk]

So, if I understand you correctly, when you installed the fuel pump kit, the motor immediately came to life and ran like you were wanting it to when you posted the first time.

In other words it ran like you had hoped WITHOUT making the jet change, but after the pump kit. Then at that point you installed the smaller jets??

Not trying to pain about this, BUT, if the pump kit fixed the problem WITHOUT the jets, then it was probably too lean to start with, or at least the way the problem was described would point that way, and starving for fuel.

On the other hand, if the motor did not come to life until AFTER the leaner jets were installed, too rich. Unless a de-laminating diaphram can cause a too rich condition which was somewhat indicated by the condition of the plug in the top cylinder. I have no experience with these motors, other than a fuel pump that is not working correctly, usually does not pump a sufficient amount of fuel. Perhaps a Merc technician will chime in here with just exactly what happens with de-lamination of the diaphram, and how that affects these pumps.

The reason I am trying to figure out what you did that solved the problem, is in addition to helping you with your specific problem, this site, and the technical forum itself, is designed to also help others and at this point I am happy you do not have a problem anymore, but unsure exactly what solved it so we can all learn from your experience.

[mercguy]

So, if I understand you correctly, when you installed the fuel pump kit, the motor immediately came to life and ran like you were wanting it to when you posted the first time.

In other words it ran like you had hoped WITHOUT making the jet change, but after the pump kit. Then at that point you installed the smaller jets??

Not trying to pain about this, BUT, if the pump kit fixed the problem WITHOUT the jets, then it was probably too lean to start with, or at least the way the problem was described would point that way, and starving for fuel.

On the other hand, if the motor did not come to life until AFTER the leaner jets were installed, too rich. Unless a de-laminating diaphram can cause a too rich condition which was somewhat indicated by the condition of the plug in the top cylinder. I have no experience with these motors, other than a fuel pump that is not working correctly, usually does not pump a sufficient amount of fuel. Perhaps a Merc technician will chime in here with just exactly what happens with de-lamination of the diaphram, and how that affects these pumps.

The reason I am trying to figure out what you did that solved the problem, is in addition to helping you with your specific problem, this site, and the technical forum itself, is designed to also help others and at this point I am happy you do not have a problem anymore, but unsure exactly what solved it so we can all learn from your experience.

Bill, when any of these pulse operated fuel pumps have a diaphragm rupture/tear, etc, the excess fuel will flood the cylinder the pulse (not vacuum as stated) is drawn from..............Yamahas are very susceptive to this problem, Mercs too.............as you might know, Merc eliminated the rubber check valves in the fuel pumps and have been using a plastic disc, since the alcohol/ethanol fuels would make the rubber disc curl up...........any time I service a Merc and it still has the paint on the fuel pump diaphragms, etc....I install a new fuel pump kit............

[Bill Van Steenwyk]

Daren:

Thanks for giving us the benefit of your Merc tech experience. I was hoping you would see this thread and chime in.

Last year when I rebuilt the lift pump on my V-6 EFI I wondered why the check valves had changed in design, from what was in the pump to what was in the kit, and your explanation about the rubber material makes perfect sense now with the comment about ethanol.

Thanks for the clarification and I'm glad the OP solved his problem.

[mercguy]

Daren:

Thanks for giving us the benefit of your Merc tech experience. I was hoping you would see this thread and chime in.

Last year when I rebuilt the lift pump on my V-6 EFI I wondered why the check valves had changed in design, from what was in the pump to what was in the kit, and your explanation about the rubber material makes perfect sense now with the comment about ethanol.

Thanks for the clarification and I'm glad the OP solved his problem.

Bill, I do have to apologize for not calling you back last year on your issue. What did you find to be the problem/problems???

PS: I owe you one!

[Bill Van Steenwyk]

Daren:
See post #17 in this thread.

[MTECHMARINE]

This is tricky, twice I thought I had too lean on carbs but was really too rich. I agree with that theory, lean it down.

[lcp]

what ratio do u guy run with the mercury 40hp seapro....i heard 1.63 kind of hard looking for props......anyone run with 1.83?