Running wayyy too rich, mechanical fuel pump?

[reggiev]

Ok guys, I have had an increasingly worse problem with over fueling going on. At first I figured it was the carb, (carter 625 4bbl), so I rebuilt that back to factory spec. Re-installed and test drove, problem was still as bad, if not worse. Engine has been misfiring like crazy and spitting black out the exhaust pipes. So my next guess was the timing. I scored a mallory billet dizzy from a friend so I figured this was as good a time as any to dial in the timing just right. So I installed the distributor, timing it to TDC on compression stroke and advanced it to around 12 ish. Engine will not fire at all, but at this point I was noticing just how much fuel was back shooting out of the carb. So I pulled all the plugs and did compression tests on all cylinders, everything checked out fine, but when I was doing this, I had the fuel line going into a gerry can and it was just dumping fuel in there. So my question at this point, can the mechanical fuel pump ever fail in the sense that it delivers too much fuel?

 

[chengny]

So my question at this point, can the mechanical fuel pump ever fail in the sense that it delivers too much fuel?

Yes. See how Popular Mechanics magazine describes it below.

But be aware that an open ended capacity test - like you did when you had the hose going into a bucket - will always demonstrate the pump's full, unregulated flow. Only when the carburetor bowl is full and the float valve closes does the pumping rate slow down. This is caused by the discharge pressure restricting the stroke of the diaphram. Read here:

http://books.google.com/books?id=D-...w back through a mechanical fuel pump&f=false

 

[HotRodPC]

I guess according to that article. But I'd have thought not being that the needle and seat would be able to shut the fuel off. I guess it could make sense if the pump was strong enough to bounce the needle every time a pulse form the pump hit hard enough. But, if the pump worked properly before, I could see a diaphram spring getting weaker but not stronger.

And you're certain your choke butterfly is OPEN and staying OPEN?

 

[reggiev]

Hmmm, at a cold choke position how far open should the primaries be? Carter 9635/ edelbrock 1406

 

[HotRodPC]

Hmmm, at a cold choke position how far open should the primaries be? Carter 9635/ edelbrock 1406

Now you're talking about the bottom throttle plate butterflies right? And are you talking at idle? Shouldn't really be open all that much, but they do need to be open at least a little bit. I guess it could be possible as your choke butterfly is closed for choke, the primaries aren't opened up enough. That is possible. IIRC, there should be a high idle screw adjustment on the high idle cam. If it's not the Eddy 1406, then I'm thinking of another carb. I've played with to many to recall for certain without looking at one now. And I'll just admit right up front, I don't consider myself good with carbs at all. Know just enough to get into deep **** and I mean that.

 

[chevyk10]

Stock fuel pump should not over power a good needle and seat. Sounds more like a float stuck or improperly adjusted.


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[HotRodPC]

Stock fuel pump should not over power a good needle and seat. Sounds more like a float stuck or improperly adjusted.


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You wouldn't think so, but according to the article Jerry posted it can.

 

[chevyk10]

You wouldn't think so, but according to the article Jerry posted it can.

Be pretty damn rare. I wouldn't put my money on it.


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[HotRodPC]

Be pretty damn rare. I wouldn't put my money on it.


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Naww, me either but stranger things have happened. I'd be more apt to think it's would be something in the choke operation. Rich not only means to much fuel, it also means not enough air, and that's where I'd be starting. Looking for a lack of air. Dirty air filter, choke butterfly not working properly etc. ESPECIALLY since he mentioned the black smoke. Getting to much raw fuel down the intake doesn't normally cause black smoke, but lack of air damn sure will.

 

[Stroked]

A stock fuel pump will over power the needle and seat in an Edelbrock/Carter more often than you would think. I've had to run a fuel pressure regulator with every Edelbrock I've owned. The stock fuel pump on my K10 puts out almost 8 psi and the Eddy can only handle 5-6.

 

[reggiev]

I've been reading on a few other forums that this is pretty common. The floats are adjusted spot on, and the needles/seats are brand new. It's getting enough air I'm sure of that, all signs point to the fuel pump at this point. I'm going to find a low pressure fpr and try that out, but first I'll test the pump and see what kind of pressure it's making, I'm willing to bet it's over 8 psi

 

[chevyk10]

Naww, me either but stranger things have happened. I'd be more apt to think it's would be something in the choke operation. Rich not only means to much fuel, it also means not enough air, and that's where I'd be starting. Looking for a lack of air. Dirty air filter, choke butterfly not working properly etc. ESPECIALLY since he mentioned the black smoke. Getting to much raw fuel down the intake doesn't normally cause black smoke, but lack of air damn sure will.

I had one of those Eldebrock carbs and it stayed rich. I thought fuel was pouring everywhere. It's probably stock with a lot of vacuum and that can lead to a rich condition in these carbs. I don't know the fix but I believe there is something you can do to fix it. If the needle and seat wasn't sealing then you would have gas pouring everywhere not just a rich condition. IMO


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