Do not plug this hole off.
As you can see there is also a hole inside the bore that leads to the other hole. When the hole on the flange is covered vacuum is fed from inside the bore. This is as expected.
This vacuum hole leads up through the carburetor and out the connection for the distributor advance tube.
I figured it out the, There was a burr on the face of the seat body that would not allow the copper gasket to seal. Filed it flat and its fine.
I made this change because fuel had been overflowing out tge vent in the top of the carb and running down the manifolds. After the fuel pump switch, the truck started and ran - and fuel promptly overflowed the bowl and again ran down the manifolds.
1st of all I think you need more than 2 1/2 lbs of fuel pressure, but that isn't your problem.
You are flooding (getting too much fuel in the float bowl).
This can be caused by several things.
Dirt in the needle & seat, float gone bad, etc.
Damage from ethanol if it sat around a lot.
Gas turning to varnish from sitting, coating the inside of the carburetor.
Fuel may be leaking around the needle & seat into the float bowl. Some kits use a metal washer on the seat which doesn't always seal well. Treat the washer with Permatex Anarobic.
The biggest problem with carburetors these days is the lousy gas, sitting around a lot and the ethanol.
I would try to blow a little air into the fuel inlet to see if you can dislodge any dirt that may have gotten into the carburetor.
Thank you! Blowing air in the fuel inlet seems to have stopped the flooding. Turned the pressure regulator up to 3 psi also.
The port in the throttle body is for the spark valve. Not all Holley 1904 carburetors have this.
This would be the normal reaction when going up to high elevation. The jet is probably jetted for lower elevation and when getting up to 7,000 too much fuel is being passed.
One possibility is that the jets are metered for sea level, which would have been the default. At 5,000 we would reduce the jet size by .002. Perhaps that has never been done. I would suspect that a jet for 5,000 would also work at 7,000.
If we had the carburetor number we might be able to find the sea level size, otherwise it's a guess.
At 5,000 watch your plugs. They should burn tan, or gray. Dark brown or black means they need to be reduced by .002.
Adjusting the idle mixture has no affect other than for idle.
Rebuilt My Carburetor But Still Floods