How can i tell if my vac secondaries are opening? i try using the "looking under hood gap" when the hood is open in the driveway but i get nothing to move... so instead i built my own mechanical linkage for it to use it at the track, works great on the street but I know it isn't right so how do i know if they are opening or not and what do i do to fix it? just rebuilt the carb about 3 weeks ago cause they weren't working then either and still no change in it at all....

Thanks for the help in advance...
Chris

 

They only work under a load, they will not move when just free revving if its working correctly.

 

The best way to tell if your vaccum secondaries are working is to unhook them, then drive it to see if it runs different.


You should not be making linkage to operate these secondaries manually, the vaccum secondary carbs do not have an accelerator pump, so they have to be operated by vaccum to prevent bogging by causing an overly lean condition.

Like what was previously posted, they will not open with the car in nuetral and you operating the throtle, they are load sensitive.

A way to see how they are working, and to improve the performance, is to tune the secondary opening rate. This is accomplished by replacing the spring inside the secondary diaphram. Once you find out which spring your carb has in it now, buy the secondary kit, and continue trying lighter(faster opening) springs until you have a slight bog, then go back to the last, one step stiffer, spring. Remember that you do not want to be able to hear or feel the secondaries open, it should be seamless transition.

 

The way Holley says to check them is to put a light paper clip on the rod that comes out of the diaphram housing and operates the linkage. If they are opening, the rod will move up and slide the paper clip down.

Dan