Vacuum Secondaries

DadsNewToy said

I've got a 340 with a Holley 750. I was disappointed with the kick when I punched the throttle. I discovered with the help of a bobbie pin that the vacuum secondaries are not opening. I adjusted the throttle cable and gained more petal travel. The difference was amazing but the secondaries are still not opening. I've looked at Holley videos but still not 100% sure the vacuum lines are correct. The PCV valve hooks to the btm rear of the carb? What do I need for vacuum pressure to actuate? Is the 750 too big. Any suggestions are appreciated.

Click to expand...

Like was said - they're called vacuum secondary because the pressure differential between one of the venture, and atmospheric in the dashpot, is what opens the secondaries. They are the better choice for most automatic equipped street cars. But most people don't understand them or try to actually set them up properly. The springs are color-coded. You buy the assortment, and follow the instructions to get one that works as you need it. Usually that's the purple or the light yellow. When they are opening properly, you will not feel them open. If you feel them, they are opening too fast.