Just installed a rebuilt Rochester carburetor that idles at 600RPM in drive which is good and I can get it to 600-900RPM in park. The air/fuel screws are three turns out from the company. Problem is when its in drive or reverse and I hit the brakes hard it stalls. The brake booster is good I did the check by pumping the brakes 4 times holding it down then starting the car which it then goes to the floor. I think its a vacuum leak but from where?
So its a 1972 cutlass Rochester 4bb carb with a 350.
What should the RPM be at in park because my manual shows 600 RPM in drive but nothing in park.
I'm new to carburetors and this is my first project car so any advise would be great thanks.

 

Take carb cleaner and slowly spray area the carb base and listen for the idle to change. You'll find your leak quick enough.

 

My website reference section has tuning tips for Quadrajet with pictures. Easy, basic tuning guide. Or give me your email address and I can send it.

Idle mixtures screws should be adjusted one at a time to highest vacuum level or idle speed. Then adjust main idle speed. This should be your first adjustment point.

Does engine stall when you are driving, or just while you are parked and hitting brakes?

 

Agreed with Qjet power....Purchase a Vacuum gauge to preform carb and timing tuning. The timing (all 3 events) and the A/F mixture all need to play together. So you need to go back-n-forth between the two to "super tune". We'll address the other two timing events later. Or search it here as many including myself have addressed it.

Lets assume the carbs OK, (internally).
Get the gauge, hook it up to a vac source on the intake or off the carb base (throttle body). For a stock 72 Olds 350 engine the A/F screws should be about 1.5 turns out from the seat. This is a general starting point. If they require more say 3 or more turns out, theres likely a vacuum leak somewhere. Adjust the A/F screws to obtain the highest possible vac reading. Then tweak the base timing for the highest reading. Then go back-n-forth to obtain the absolute highest vac reading at warm curb idle (650-750 RPMS). The vacuum gauge should be a steady 18-22" of vac for a well tuned, stock, healthy 72, 350.
Common vac leak sources are:
1. Wrong, improperly installed or damaged gasket under carb.
2. Internal carb leak. (over torqued)
3. Brake booster, its vac line or the rubber bushing on the one way check valve or the rubber gasket behind the master cylinder. The brake pedal will also be hard.
4. The distributor vacuum advance canister.
5. All vacuum lines in the engine compartment can be suspect.
6. Worst case it could be bad intake valves or intake gasket.(fluttering vacuum gauge)

Did it run OK before the carb rebuild?
How many miles on this engine?
What other work was preformed?
How does the exhaust note sound at the tail pipe(s)?
What style and thickness is the carb to intake gasket?

Cap off all the lines to the carb including the power brake line. Try to tune. If it still wont tune with everything capped off then its the carb, carb base or throttle body to bowl gaskets, intake gasket seal or intake valve problem. If it cooperates with everything capped off, great. Now one by one hook the vacuum devices back up until the bad circuit shows itself and correct.

Careful not to over torque the carb. It warps easily when over torqued. Re-torque after several heat cycles or 500 miles.
When seating the A/F screws seat gently. Over torquing the AF screws will damage the seat and screw taper.

 

x2

The vacuum source needs to be "manifold" vacuum. In other words, there should be vacuum when the car is idling.

BTW, you can usually rent a vacuum gauge from your local auto parts store.