mach12450

Well RBOT I hope you had good luck. I found out that part number doesn't fit my block or fuel pump so I couldn't use the gasket. Put a Sierra pump on for a 90 7.4 litre ran fantastic no issues so far. Mercruiser should be ashamed of themselves.

SB

iTrader: (1)

It's probably for a small block pump, as the mounting bases are different size from sbc vs bbc.

But as I said before, this is a BS attempt from Merc anyway.

BUP

iTrader: (9)

1 is that gasket 27-431861 is to thick anyways also it is the gasket / spacer / insulator for the mechanical fuel pump used on carb 3.0 Mercruiser apps thru out many years. Not even the same fuel pump used for V 8 engines (small and big blocks).

This has been a problem for the past 4 or 5 years so nothing new as the fuel pump is being overstroked causing high pressure 10 to 14 psi.

Sierra and Mercruiser mechanical fuel pumps are made by the same companies. Airtex and Carter. I talked to both companies in person about who makes what for whom. Verified its the same pump just that sierra did not and or does not paint them black as Merc does or did.

We made our own spacer half the depth of Merc 27-431861 about 4 or 5 years ago when the problem first started. These apps are still running today with about 6 psi to 6.5 psi of fuel pressure without problems. At that timeframe Sierra fuel pumps did the same - over stroked causing high pressure.

We tried about 2 or 3 of each brand and all did the same No difference between Sierra & Merc.. Currently so far out of the box I have not seen this problem like in the past. Really currently I do not see that many carb apps using a mechanical fuel pump like in the past.

Anyways at that timeframe in the past we really had nothing else to do but make our own spacer and gasket the spacer on both sides. Like I said it still working just fine running 6 to 6.5 on about 12 to 14 apps that I seen yearly here and there.

Even if its a band aide we did not have any other options at that timeframe.

SB

iTrader: (1)

I understand. You have to do what you have to do, but this is something no on should have to do.

This stroke thing kills me.

It's the big diaphragm spring that sets the fuel pressure.

See diagram:

SB

iTrader: (1)

On the Holley rebuildable pumps, as an example, you can get a low psi or high psi version. Just a spring change.

Low psi:


High Psi:

RBOT

Thanks I did. I ended up plumbing in a fuel pressure regulator and gauge. Set it 5.5 psi and it runs perfect. Agreed with what everyone else says, no way should we ever have to do this with stock merc parts. When I returned the gasket, I told the guy at the store about what I was going to use the gasket for and what I ended up doing. It opened up his eyes for sure, that merc would tell anyone to just run a gasket to "fix" the issue.

Good to see that you are up and running as well.

mach12450

Good deal! I think that's what I'll do if I have any more issues, such a terrible ordeal all the way around but glad we are out enjoying the water. Where did you get the regulator?

edwardpdaly

i have been reading these threads as i too have had issues with the fuel pressure. I had flooding issues at idle after having the carb rebuilt. I took it back to the repair guy and he put it on the flow bench and showed me that at less than 7 psi the cab does not leak, hit 7 and it leaked. He reset thing and ran it at 5, no leak, 6 no leak, 6.5 no leak, hit 7 and it leaked and filled the carb. I went home and tested the fuel pressure again and it was at 7. removed the fuel pump and noticed there were two small gaskets there, removed and installed the thicker gasket i got from the boat store, a merc part, and retested the pressure and it came in at 5.5. installed the carb and after a rough start it ran well. set the idle mixture screw, 1.25 turns, and the idle screw and it ran better. adjusted the idle screw, and idle mixture screw to get the desired idle running on garden hose at home. i set it at 1000 rpm, will come down when in the water at idle and will reset both the idle air mix and idle screws once more. i suspect the final idle air mix setting will be more like 1.5 turns with ldle set at 900. Going to head out sunday to test the boat and give it a good run before fall bass season in NJ.