Vacuum Operated Holley 750 Question

[Paul Cotton]

I have a 440 ci engine with a Bullet cam in it, Edelbrock Performer 440 intake and a Holley 750 vacuum carburetor. Needless to say, this setup creates a vacuum problem due to the cam. I have done the paper clip trick on the Holley vacuum secondary and it seems to be opening. However I am not convinced the carb and motor are operating properly. I was wondering if the lack of vacuum is impacting the Holley secondary. I put a weaker/lighter spring in the Holley secondary and it seemed to help but I am still not happy. I have installed a SSBC vacuum pump and reservoir to handle the power brakes. Should I be looking at installing a T fitting in the vacuum line and going to the intake manifold with it. Would this help the secondary coming on line or would it negatively impact the engine performance?

 

[66chargerpat]

Manifold vacuum doesn't pull in the secondarys. The diaphragm gets it signal from the pressure drop on the primary venture . The faster the incoming air, the greater the pull on the diaphragm. Vacuum sec. carbs only open when there is a demand for more air.

 

[lewtot184]

holley vacuum secondaries rely on the air velocity in the driver side primary bore. the size of the passages will dictate opening rate as well as the spring. i'd look over the carb to make sure there isn't any problem in the vacuum passages. you could have a basic tune-up issue; ignition timing/fuel flow.

 

[Tempest 455]

1st question. What Holley 750?

 

[LemonWedge]

If you have a hand vacuum pump, Hook it up to the diaphragm. When you squeeze the vacuum pump, if the secondary's open, it's working.

 

[Paul Cotton]

1st question. What Holley 750?

It's the classic 750 Holley, 4160C, vacuum secondaries and electric choke.