Carb vacuum leak - best way to seal?

[C10Silverado79]

I seem to have a vacuum leak at the rear of my carb where it mounts to the manifold. The carb was rebuilt, the gasket is new and the bolts are torqued down properly. The front seems to be fine but the rear definitely has a leak. What is the best way to seal the leak? Add some gasket sealer? Go for another new gasket? Something else?

[GMC Guy]

maybe try adding a couple thin gaskets? just an idea.

[cableguy0]

What kind of carb and intake is it? If your using a sqaure bore carb with a spread bore manifold such as an edelbrock performer with an edelbrock or holley square bore carb your supposed to use the square bore adapter plate to ensure a good seal.

[dammitmitchell]

by what means are you declaring it's a carb leak?
if you are spraying WD-40 or anythin like that back there to see if there's an idle change you might want to explore the rear gasket on your intake.

when you pulled the carb last did you inspect everything make sure all lines not in use are capped etc?

[C10Silverado79]

Sorry, It's a stock Q-jet 4bbl. I put a new gasket on when I rebuilt the carb a month or 2 ago. I also replaced all the vacuum lines. Yes, the idle increases and smooths out when I spray some carb cleaner around the back of the carb (near dizzy) where is mates to the intake manifold. I had cleaned both surfaces before putting the carb back on.

[silvereagle07]

I'd go for the new carb gasket. But check with a straight edge to see if the manifold or the carb base is distorted. The should not have much clearance at at all.

[ron350]

Is it possible you used the wrong base gasket for your carb?

[C10Silverado79]

Originally Posted by ron350

Is it possible you used the wrong base gasket for your carb?

I'm not beyond making a mistake so it's possible. i know I tried to match the old gasket with the new ones to get the right match. I guess I'll get a new one and see if that solves the problem.

[p_rubottom]

Kinda a shot in the dark here but could run a bead of gasket maker on your paper gaskets you have installed already just to make sure theres a good seal?

[Dropped84GMC]

what i do is run over the gasket areas with a sharping stone just to smooth and level them out ... my advice is to buy a new gasket and do what i said above and see if your problem is fixed ... also i would put a rag in the intake manifold and use a vaccum cleaner to suck out all the little chips from where you sand the intake manifold

[cableguy0]

Rtv should not be used on a carb gasket. As stated make sure the surfaces are flat and make sure your using the proper gasket and theres no reason it shouldnt seal.

[irishman999]

My quadrajet has a pretty strong baseplate, im not sure if it would warp easy but i've seen carbs that got overtightened and it warped the baseplate, in that case i would secure the carb in something like a vice, wrapped in a towel and file the bottom with a large bastard file.

[C10Silverado79]

I'm pretty sure I resolved the vacuum leak. I decided to poke around a bit before i tore the carb back off. Turns out the diaphram in the EGR valve is shot. Since the valve sits right next to the carb I think it was picking up the carb cleaner when it sprayed. I disconnected the valve and capped the line. Carb cleaner made no change and vacuum is steady. I don't know if I'll replace the EGR or just leave it disconnected.

I still have to solve my problems when motor is under a load. My first thought was the it wasn't getting enough fuel. I'm starting to think it's "Fuel Spewing" instead but I'm not sure how to fix it.

[dammitmitchell]

fuel filter first

[68 TT]

Originally Posted by C10Silverado79

I still have to solve my problems when motor is under a load. My first thought was the it wasn't getting enough fuel. I'm starting to think it's "Fuel Spewing" instead but I'm not sure how to fix it.

It is possible you set the float level too high when you rebuilt it. Kind of a pain to readjust on a Q-Jet.

[C10Silverado79]

Originally Posted by 68 TT

It is possible you set the float level too high when you rebuilt it. Kind of a pain to readjust on a Q-Jet.

Certainly not 'IMPOSSIBLE'. I'm going to triple check everything else first before I pull the carb apart again. I went back and read some more in my Doug Roe book which is why I'm leaning towards fuel spewing more than fuel starvation.