Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Leaky Inlet Frustration

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Cliff Ruggles:
Good news!  I was hoping that you could get the fuel filter housing to seal up without having to "spot-face" the sealing surface.

Also good new on getting the bottom plugs sealed up and the carb working correctly......Cliff

Shiny:
Well, I celebrated too soon.  After sealing the bottom plugs, the car started and idled well, so I moved on to attack power steering, which now seems to be working.  Today, my son and I went out to bleed brakes so we could drive the car and check out the carb.  I had to crank a lot, which made me nervous about the leak again, but it started fine after the carb got some gas.  After warming up the engine, I pulled my plug off the vacuum port at the rear base of the carb to put on the brake booster hose and liquid gas puddled out of the fitting.  I had my son push the pedal to the floor and hold it, and there seemed to be a lot of fuel vapor coming up from the manifold....

So I pulled the carb again, and sure enough, there is still a gas leak from somewhere.  The gasket was visibly soaked.  As I lifted the carb, there was a drip and the base seemed wet in general.  I tilted the carb a little toward the choke side, and gas pretty much poured out...

So now I am getting even more frustrated, but really, I guess it is more a case of being humiliated by something so seemingly simple.

I tipped the carb upside down to pour the gas out, then checked the inlet again with my vacuum pump.  It held vacuum fine, so I don't think the float is the root of this problem.  I must have another leak somewhere or I used the wrong gasket or something??  arrrrgggghhhh

Any suggestions as to what I should look for this time?  Some things that may be related:

1.  the plastic baffle has been cut off the bottom, presumably to allow more gas in the bowl ??

2.  I set the float height at 1/4"...is that too high for this carb (29240MD) ??  Is there a chance fuel is spilling over somewhere ??

3.  I got pretty aggressive removing the APT screw from the base.  I heli-coiled it and used your replacement screw... all seemed fine.  Is there a chance I could have drilled through something or left the APT spring too high and somehow created a fuel leak??? 

I guess I'll pull the top off and fill the bowl with gas or something else and see if I can see a reason.

Any suggestions on how to solve this (finally, really) would be greatly appreciated.

Cliff Ruggles:
Did you pressure test the bottom plugs while the carburetor was apart?.....Cliff

Shiny:
On my original attempt to diagnose the leak, I put a tapered air nozzle with about 50psi behind it into the 2ndary metering orifices where the rods go, but I could not totally seal the pressure, as there are many ways for the air to go... but with whatever pressure I developed inside the well, I did not see bubbles with soap, yet that is the location of my original leak (or at least where the gas was dripping).

So without ever confirming the leak, I went ahead and drilled/tapped/sealed with marine epoxy on all 4 wells.  I used set screws on the small ones and cut up a 7/16" bolt to fabricate plugs for the big ones.  I did NOT try checking with my air nozzle again, because I didn't detect a problem the first time.

I will pull the air horn and try again to verify my seal was effective, this time I'll try to make sure I get pressure built up on my new plugs.

Is there a better way to pressure-test these seals on the wells?

I am still suspicious I have another problem, so I will also fill up the bowl with solvent and look harder..

Is there another "common" path for leaking besides the seals?

I guess I will pay more attention to the gasket sealing surfaces too...

Thanks for eliminating the float height as a possibility.

Shiny:
Pressure-tested plugs I had installed and no leaks.

Filled the bowl with gas, covered with saran wrap to slow evaporation, let sit for 30 minutes on a paper towel, and no leaks...bowl was still filled, towel had no spots, plugs looked dry.

So I am baffled, stuck, and just about out of ideas.

Seems like I must have a float problem, but the inlet valve seats fine with vacuum (new valve and float from your kit).  My pump is mechanical, so I don't expect the pressure to be high, but ??? is it possible for a mechanical pump to have too much pressure?  what is the best way to measure?

Is there some other reason a float might stick?

I will try lowering the float a little too, but I just can't find a reason for the leak or overflow or whatever is behind this...

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