When you open the throttle all the way with your hand, the primary throttle will open directly with the movement of your hand on the external linkage on the driver’s side of the carb. The secondary throttle is vacuum operated on that Holley so the engine will reach a certain RPM and it will roar like a lion, then the the secondary throttle will open, by means of vacuum, or indirectly, and the engine will gain RPM and scream like a raped ape!
At this point, you will let go of the throttle to avoid over-reving the engine.
Importantly, with a 4 barrel carb that has vacuum operated secondaries, the secondaries will not open without vacuum. In other words, they they will not open if the engine is not running.
This is confusing – A 4 barrel carburetor like yours has two throttles, butterfly throttles in the base plate of the carb which lives directly above the intake manifold, but everything connected to those throttles, such as the external linkage as well as the “gas pedal” inside the vehicle, is also called a “throttle”.
In other words, if you drive like Grandma, you control the primary throttle with your wee footsie on the gas pedal and the secondary throttle never opens. When the teenage grandson borrows the car, he nails the pedal to the metal and the primary throttle opens all the way, then the engine gains RPM until vacuum opens the secondary throttle and the police pull him over.
- Home
- 4brl holley problems