Engine stalling after warmup

[eoseitz01]

I'm currently building a new engine for my 74, but I'm wanting to figure out this issue before I swap engines in case it's not the old motor.

When I start up the car it runs fine. I can take it up the road a few miles no problem. However, once it warms up it wants to stall when you stop or turn. I have to use the hold gas and brake approach to get it back home.

Before I started my engine build I changed out the fuel filter, carb and rotary cap/button. It still does it. Could it be a bad vacuum advance? I'm using the distributor on my new engine so I hope it's not. I also noticed a hissing sound coming from the brake booster area when I shut it off. I changed out the hoses and the check valves. I also changed the check valve on the valve cover because it looked old and crumbly.

Any ideas?


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[eoseitz01]

I should mention its a 350


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[Antz81]

the hissing will be a vacuum leak. Below the brake booster will be an Evap cannister. Check this and the hoses to it for leaks.
If a vacuum leak is large enough it can cause issues with your idle.

 

[LLC5]

Pinch off or disconnect and plug the vaccuum line to your brake booster and see if the problem goes away, if it does you need a new brake booster. You should not hear any loud (very audible) hissing with the engine off. Good luck with it.

 

[eoseitz01]

Well the evap canister doesn't appear to be connected. The hose to the fuel line is there. I plugged it back in, but the carb line is nowhere to be found. Which port on the carb does this go to? I have two on the front. One is plugged and the other goes to the vacuum advance. I'm guessing it can't be leaking if it's not there.

I replaced the hoses, check valve and grommet to the booster. I still hear a hiss when I shut the car off.

I can pump up the breaks with the car off. When I start the car, hold the break and shut it off, the pedal comes up after about 5 seconds. I'm thinking it should be 30 or more. Sounds like it's probably my booster.

On a side note, when I was checking my break booster I noticed the mount under it is about half rusted. Is this a body mount or part of my frame? What issues will this cause?


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[eoseitz01]

Engine runs much better after plugging booster. Shifts normal again too. Will a break booster off any other vehicle fit or is it corvette specific?


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