Thread: Low engine vacuum but no vacuum leaks.

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Originally Posted by 47Fordcoupe

Hello everyone, I'm new here.. hoping someone could help me figure this out. So I recently purchased this car which has a 305 SBC in it. The engine starts right up when cold, but hard to start when hot. I already ruled out vapor lock as well as engine vacuum leaks. My vacuum gauge is fluctuating between 5" Hg an 7"Hg.
Also my timing seems to be way advanced at 30* at idle and I can't bring it down without the engine stalling.. I did find tdc and checked harmonic balancer mark. Thanks in advance for your inputs.

First thing I would do is to change spark plugs and install a QUALITY set of spark plug wires, along with new distributor cap and rotor. Inspect the interior of the distributor to insure that the weights are free to swing out and advance timing and that the vacuum line from the vacuum can to the distributor is free of cracks or holes. The vacuum, with a stock to mild hot rod cam, should be at least 15" Hg and the needle should be steady. Here's a tutorial for you to follow.......
https://www.youtube.com/watch?v=SdlNwm8OHco

Once you are through with the vacuum tests, do a compression test of the motor.
Run the motor to bring the water temperature up to max
Remove air filter assembly
Use wire or string to tie the throttle wide open so the motor can breathe
Number all spark plug wires and remove all spark plugs so the starter won't have to labor to turn the motor over
Disable the coil so that you don't have any sparks to start a fire
Key the starter and let the motor go through at least 5 compression cycles for each cylinder, as pressure builds on the gauge
https://www.youtube.com/watch?v=X_tbksFYhl4&t=168s
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