Weber 4 barral carb loading up with fuel

baycruiser · Sep 20, 2010

I have a 1995 5.7 Mercruiser with a 4 barrel carb and a Alpha One outdrive. I have just bought a reman long block and installed it in the boat. The engine starts right away, but idles at 1100 rpm and within a few minutes loads up with fuel and will choke out unless reved up to burn off fuel. As far as I know at idle fuel should only be delivered by the metering rods not from the top. this was an existing problem before but not as bad. Thanks for any suggestions.

Don S · Sep 20, 2010

Re: Weber 4 barral carb loading up with fuel

Go through this Merc service bulletin on the Weber carbs, I'm sure you will find your problem.

http://www.boatfix.com/merc/Bullet/97/97_09.pdf

Aloysius · Sep 20, 2010

Re: Weber 4 barral carb loading up with fuel

idle fuel is only metered through the transfer slots/holes next to the throttle plate. Transition to main metering should occur above 1500 rpms.

baycruiser · Sep 20, 2010

Re: Weber 4 barral carb loading up with fuel

I just rebuilt the carb and the float evel and drop are to specs. Sight tube is clear, but I had thought of checking the pressure of the fuel pump, although I wouldn't think a mech. pump would run high pressure.

John_S · Sep 20, 2010

Re: Weber 4 barral carb loading up with fuel

baycruiser said:
I had thought of checking the pressure of the fuel pump, although I wouldn't think a mech. pump would run high pressure.

I use to think the same, but after measuring found out differently. Check it.

baycruiser · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

I hooked up a fuel pressure tester and it pegged out at 10 psi. The pump was new last season. Would you sugggest a pressure reg. or new pump? Are inexspensive regulators as good as exspensive ones?

John_S · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

baycruiser said:
I hooked up a fuel pressure tester and it pegged out at 10 psi. The pump was new last season. Would you sugggest a pressure reg. or new pump? Are inexspensive regulators as good as exspensive ones?

I looked, but didn't find a very reasonable marine rated regulator. Plus you need to hard mount it and run marine approved lines. I just bought a new pump.

Aloysius · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

What kind of pump?

baycruiser · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

It's a mechanical pump. It was suggested to me by a parts man who deals with Mercruiser to try a thicker gasket. Mercruiser told them to try it a couple of years ago when their shop had a similar problem. Going out to try it now.

John_S · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

baycruiser said:
It's a mechanical pump. It was suggested to me by a parts man who deals with Mercruiser to try a thicker gasket. Mercruiser told them to try it a couple of years ago when their shop had a similar problem. Going out to try it now.

Interesting. It wouldn't have expected that would change the pressure significantly. I'd be interested in the results and what the difference in gasket thickness was. And which one, pump only or mounting plate to block gasket.

Alpheus · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

A thicker gasket will lower the pressure, but if you are pegging a 10 psi gauge I don't think it will lower it enough. Weber/Edelbrock carbs are very picky about inlet fuel pressure. If the thick gasket doesn't work, get yourself a new marine fuel pump or get a block off plate and install an electric one.

I hope it works out for you. Good luck...

baycruiser · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

I couldn't find a thick gasket today so I used two homemade cork gaskets. It ran much better but still was pushing eight psi. Since I can never leave good enough alone I tried a third. They just started mushing out between the pump and the block. I still would like the pressure between 4-7 psi so I am going to the speed shop tomorrow and find one thick one.

Don S · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

You shouldn't need to be spacing out a fuel pump to get the correct pressure that is nothing more than a bandaid fix at best. Was this a marine fuel pump or some High pressure fuel pump for racing?
You really want a marine pump. Fancy racing pumps, even if marine, are not needed on your engine.

Aloysius · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

I've been wrenching for 40+ years, and I've NEVER heard that gaskets affect fuel pressure. But, hey, if it works...

I DO KNOW that if you put a 2" thick gasket in it you won't have ANY pressure...............

Alpheus · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

I guess you never worked on flathead V-8 before then. New pumps come with different thicknesses of gaskets to adjust the fuel pump pressure...

Don S · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

Alpheus said:
I guess you never worked on flathead V-8 before then.

We're not discussing Ford flathead V8's here, we are discussing 1995 Mercruiser Chevy 5.7 V8 engines, and they DO NOT come with spacer gaskets for the fuel pump.

When you use the correct parts, they work, when you try to cheap out or half azz it with automotive parts, then things go bad quickly.

Aloysius · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

I just realized you gotta be talking about the BODY of the pump, where the diaphragm is. That's not something I'd be screwing with on a boat, I don't think. Too big a chance of leaks!

John_S · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

Aloysius said:
I just realized you gotta be talking about the BODY of the pump, where the diaphragm is. That's not something I'd be screwing with on a boat, I don't think. Too big a chance of leaks!

He indicated it was between the block and the pump.

baycruiser · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

Just wanted to clear up a couple of things. I believe this to be a perfectly good fuel pump. This is a new reman jasper long block and for what ever reason the old fuel pump (11 months old) does not like the new block. It's not my intention to cheap out but if something works within reason I'm open. Safty first.

Aloysius · Sep 21, 2010

Re: Weber 4 barral carb loading up with fuel

There should be a pressure relief valve in the pump..the gasket between the block and the body just reduces the length of the stroke, or the pre-load on the pump arm. Sounds like a band-aid solution for the real problem.

Y'know, someone on another forum had the same problem with a big block pump. Ethanol screwing with the relief valve???

Weber 4 barral carb loading up with fuel

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