This carburettor flooding issue is driving me crazy.
The carburettor now floods fuel out ot the adjustment/inspection hole on top.
I have replaced the needle and seat, verified that the float level is ok and that the float does not leak.
At idle gas leaks through the hole in the top and this indicates that it is flooding.
When I pull the accelerator the level drops a little bit before it rises again upon idle and gas comes out.

I am starting to suspect the fuel pump seeing from my receipts that it was replaced på PO in 2019 and the odd thing is that, based on the part number, it seems to be a muscle car mechanical fuel pump.

Carter M6626 Carter Muscle Car Mechanical Fuel Pumps | Summit Racing

Based on what I read it puts out 7,5 - 9 psi, but I believe that the SBC's should have from 5-7 psi to the carburettor.

Any ideas or opinions will be greatly appreciated.

 

Buy a fuel pressure gauge and check it. If the pressure is too high, install a regulator.

 

Did you remove the Float, inspect it for Holes (with a Hole, it can fill-up and sink) and make certain that it actually floats?

I am not sure what you meant by the Float not leaking... ?

 

that is the correct replacement fuel pump

I'd replace the float, and while you're there take some pics of the needle/seat hanger assembly and post them

 

What I meant is that when I submerged the float in water no air bubbles were visible.

 

Latest update now. Installed a fuel gauge and a reduction valve.and now no fuel comes out of the top of the carburettor so seems to have fixed the problem.
Have not test driven the car yet so remains to see if any unforeseen problems have been introduced.

 

how is fuel getting to the carburetor?

should flow from the block mounted fuel pump through a metal hard line that either runs behind or adjacent to the water pump.

the block mounted fuel pump should be fed by a steel line that runs atop the fender well below the liquid line AC which I see in your photo. Also missing appears to be the fuel return line.

the metal fuel feed and return should be connected to the block mounted fuel pump by short sections of rubber fuel hose.

lack of adequate return will cause the symptoms you were experiencing. if you're deadheading the fuel feed through a regulator with no return you still may have hot soak issues.

 

Go to the local parts store and get a stock replacement pump. As you can see, they're stoooooopid cheeeeep. Not worth sweating over.

And WHATEVER ELSE you do, GET RID OF that death trap rubber line. Unless of course, you just really want to burn your car to the ground when it bursts. I'm pretty sure you can get a brand new steel one, all pre-bent and ready to drop in, from the various tubing vendors.

If it still screws up, you may have a strange issue in the carb, that I've had the pleasure of enjoying myself acoupla times over the years: dissimilar-metal electrolysis between the brass needle valve seat, and the chinesium fuel bowl casting, which EATS holes in the casting including dissolving the threads. No needle & seat in the known universe can seal off the fuel flow, if there's pitting and whatnot that allow fuel to bypass it.

 

Thank you for the advise, I will check whether there are any problems with the return line.

 

I couldn't really quite decide whether to go for a new pump or a gauge and reduction valve. Then I went for the gauge simply because I wanted to find out what causes the problem.
I know a new pump is dirt cheap, but I hate not knowing and this pump was installed in 2019 so it's not very old.
Is it originally a metal line from the pump to the carburettor and no rubber hose inbetween? All this was done by PO so uncertain how it was supposed to be.

 

Yes, the original line is a piece of steel tubing with flare nuts at the ends. No rubber hose whatsoever.

It's possible, but quite difficult, to make yourself; particularly at the pump end. If the smog pump bracket is still there, it's right in front of the exit from the pump, and the bend has to be real sharp. No hand-operated tubing bender I've ever had can bend close enough to the end of the line, since the nut has to be there too. (the one I have that comes the closest is a Snap-On one) Likewise, a 90° adapter to get from 3/8" inverted flare to 6-AN doesn't fit well either. Best to just buy a pre-bent one from somebody that has machinery to do it.

It goes behind the WP and the alt. I'm pretty sure the WP has to come off to install it but you might be able to snake it through there without damaging it.

In my car, I was able to make the bottom half of it when I needed one, since I had removed the smog pump and put a bolt in the upper hole where the FP drive rod passage goes to prevent a leak; but to dodge the WP issue which I didn't feel like dinking with at the time, and had the -AN parts laying around anyway, I made a 6-AN PTFE line for the top half, and flared & adapted at the top of the steel line piece to connect the AN line to the steel brake line piece. I would NOT recommend using regular -AN line for this; ONLY the PTFE lined version. It's WAY eeeezier to work with than the neoprene or whatever it is anyway, even though a bit more $$$.



Unfortunately I don't have a photo of the steel piece.

The long and short of the problem is though, either the pump or the carb is farkled. Your task is to figure out which one. You're convinced the carb is OK; doesn't really leave much to chance. "2019" is irrelevant. Either it's good or it's not.

I suppose it's also not impossible that the return line is blocked. You might want to make sure you can blow through it into the tank. Take off the gas cap and see. It should require basically zero effort to blow into it.

 

Thank you for your feedback. I will add this to my list of items to replace in the future.
Someone have been very fond of rubber lines instead of original steel lines for whatever reason.
There are currently rubber lines from the tank to the pump and back.

I assume this is original 5/16 steel line.?

 

the original plumbing from the tank for the LG4 was:

steel 3/8" feed line and 5/16" return routed along the left side of the car up to the transmission, then crossing over the top of the trans tunnel to the right side, up and along that inner fender panel to terminate into two short rubber fuel lines to the block mounted fuel pump.

steel 5/16" vapor line following the same routing but not crossing over the trans tunnel to terminate near the charcoal canister behind the left headlight bucket.

from the fuel tank sending unit, each of these was connected with a short section of fuel hose from the steel sending unit lines that dropped down from the tank. these sections of fuel line should be accessible without removing the tank or anything else.

from the tank sending unit there is a fourth steel line that is connected to a pressure relief valve mounted near the tank, connected again with a short piece of fuel hose.

Replacements for each should be available. but may be best to ensure you have the 'stock' sending unit steel lines hanging down in back. who knows what who knows who could have done with any of that.

 

in addition, were you to go about replacing the steel lines, there is a little brace piece that holds the lines above the trans tunnel. if you don't have it you may want to look for it before any garage work is done. pretty sure there are a few other braces/brackets along the frame as well....

 

Sounds like this will be some work to do when the summer season is finished.
Today I replaced the left valve cover gasket to stop some oil leaks and replaced all spark plugs.
Nice to be hear how quick it starts now and no smell of burned oil on the exhaust pipe any more.

It still idles rough, but better than before.
Monday exhaust is planned.

Thanks guys for your help.

 

I am dealing with a similar issue. I was able to blow through my return line (fuel tank cap removed) but it takes a substantial amount of effort. Could this be the cause of excessive fuel pressure, or would it have to be completely blocked? I still need to test fuel pressure from the pump discharge, but the fact that it took so much effort to blow through the return line has me concerned...

 

What size/ diameter is your Return-Line?
What size/ diameter is your Supply-Line?

Do you have a EVAP-Line, Canister, Vented Fuel-Tank Filler-Cap, or other?

What is the approx. Flow Rate of your Pump... and at what Fuel Pressure is that Flow Rating at?
Are your Fuel Filters rated to flow more than (or at the least the same amount) as your Fuel Pump?

How is your Fuel Pressure regulator/ Fuel System arranged?


Or:



Different Model Fuel Pressure Regulators may be partial to one arrangement or the other.

 

It's arranged in the 1983 factory stock arrangement.
Has a vapor recovery cannister but is not yet connected to vacuum (tied into PCV hose).
Haven't yet tested pump discharge pressure but will do that soon...

 

It's possible, but quite difficult, to make yourself; particularly at the pump end. If the smog pump bracket is still there, it's right in front of the exit from the pump, and the bend has to be real sharp. No hand-operated tubing bender I've ever had can bend close enough to the end of the line, since the nut has to be there too.