I have a 72 that I can't get running. The car will idle, but the rpm's vary. It fluctuates between 1000 and 1100 with the idle screw all the way in. When I put it in drive, it runs real rough and eventually stalls. I thought it was a carb problem so I had it rebuilt. That didn't help. The timing is set correct and I have around 20 hg of vacuum. Does anyone have any suggestions? Any help would be appreciated.
Thanks

 

You've got a vacuum leak from somewhere.

1/Is your throttle shaft okay on the carb ? Try squirting some oil on the shaft ends to see if it gets "sucked" in. If the oil gets sucked into the carb, it's worn throttle shafts.

2/ Check your vacuum lines with a MityVac tester to see if there are any leaky vacuum hoses or diaphragms in the distributor vacuum advance canister, EGR valve, headlamp vacuum lines. Any hose connected to the engine for vacuum should be suspected.

3/ If you hear a hissing sound from inside the car even when you apply the power brakes, the power brake booster diaphragm might be leaking & in need of replacement.

Hope this helps.

 

I thought it may be a vacuum leak too, so I disconnected all the lines from the manifold and carb, and capped the ports. I also thought the carb rebuild might not be good, so I took it back. He re-checked everything and said the carb is perfect. It could be a vacuum leak at the manifold gaskets, but at 20 hg, that seems good. I'm at a loss. Thanks for your suggestions.

 

Sounds like you carb floats are not set right.
Car will idle like crap and stall out.
Just because the carb was rebuilt doesn't mean they are set right.
The floats need to be set with the car idling.

Schoon

 

Also try checking if the carb gasket to intake manifold matches both the carb and the intake surfaces.
I have found in the past that different manufacturers put out different size gaskets and experienced one that didn't match and caused a vacuum leak under the base of the carb.

 

OK Thanks for the replies. It was running very lean. I adjsted the air/fuel mixture screws out, and it's running much better. I must be leaking vacuum from somewhere because the screws are out 5 turns. That seems like alot. All the vacuum ports are capped off, so it must be the carb gasket or the manifold. I'll have to do a little more digging. Thanks Again.

 

Try setting the floats

 

Well there is only one float on a Quadrajet, and I've never heard of being able to adjust it with the car running. I would assume that the float would be adjusted properly, when it was rebuilt. Can you elaborate on how this procedure is done? Thanks

 

You have to do it w/ the top of the carb off. With one finger, you gently push down to seat the needle while pushing down at the float pivot point, then measure the drop at the end of the float and bend the float arms where the notches are to set to the distance specified in the service manual.

 

Sorry, I thought you had a Holley Carb.
I am sure the Quadrajet would have the same problem if not set right.

You might want to invest in a 1966-1982 Corvette Shop Manual.
This is the bible for these cars and it will answer most of your questions.
For example the manual says for Engine stalls:

Incorect choke adjustment
Idle mixture to lean
Incorect carburetor float setting
Leak in manifold
Distributor contacts
Burned rotor
Incorrect ignition wiring
Bad coil or or condensor
Incorrect tappet lash
And so on

Hope this helps

Schoon