Hi guys , having a problem that I can't figure out. 69 cutlass with 350 running a Holley 770 cam carb. Brake booster Vacuume port is on the back of the carb and I'm getting gasoline into the booster! Can anyone explain?

Frustrated

 

You have an issue with your carb. There should only be vacuum on that port, I'm assuming the fuel vapors are getting into the booster when the engine is turned off.

 

Actually, any vacuum comes from the intake manifold, where there is fuel. Reversion (pulsing of the intake charge in the runners due to valves opening and closing) causes the fuel/air mixture to move back and forth in all the lines connected to the intake manifold. The most likely cause is that the check valve at the booster vacuum inlet is bad. This check valve is supposed to prevent any flow into the booster.