Vacuum problems

[daler63]

I have installed a 351 windsor and matching C6 transmission in my 78 F100.The only modifications to the motor are the Edelbrock performer intake and 600CFM carb.I have tapped a vacuum port on the rear of the carb to run the Transmision vacuum modulator,brake booster and AC.The problem is this,during acceleration the airconditioning controls seem to lose vacuum and the transmission shift points are not stable,also the brakes seem weak.Anyone else have this problem with aftermarket carbs,any help will be appreciated.

 

[Dirt racer]

You should be using the intake for the vacuum for the trans, brake and interior stuff. The carb vacuum is only for PVC and vacuum advance for your distributer. It works oposite of your intake vacuum. Your intake is high vacuum at idle and your carb is high at WOT. Wide open throttle.

 

[RawkDawg]

You should be using the intake for the vacuum for the trans, brake and interior stuff. The carb vacuum is only for PVC and vacuum advance for your distributer. It works oposite of your intake vacuum. Your intake is high vacuum at idle and your carb is high at WOT. Wide open throttle.

Dirt Racer is right.......

Also your AC will default to defrost mode when it suffers a vacuum loss.....by that I mean when your HVAC unit loses vacuum all vent doors will direct air to the defrosters till vacuum returns. Vacuum loss may happen when you mat the loud pedal, stomp on the gas but will return when engine load lessens.

Also make sure you have no vacuum leaks around intake and carb. This can be done by spraying Carb & Choke cleaner around base of carb and around intake. If a change in RPM is noticed then you have a leak. Usually, the RPM will slightly increase when leak is sprayed with C&C cleaner.