Hi I have a 305 v8 with a 4bl carb that came with it, and the first two open up fine but th second set wont, they will open up and work manually with your hand but not by there self, anybody know the problem

?!?
Is this a quadrajet carb?
If so, the secondary throttle blades will open with your hand (you'll have to hold the air blades open to see it...). That is, if the carb is warmed up enough to be off choke, otherwise there's a tang that keeps your secondaries from opening.

Once the car is running, I have a hard time believing that you can tell if your secondaries are opening or not. They will be.

and you can't really get them to open sitting in park...they usually have to have a load on the motor before they really open up....revving it in neutral doesn't work.

Ok

i know this is a old topic, but both of these assumptions are incorrect.
Secondaries can be seen opening sitting still. The secondaries will only open at WOT, pinned to the floor. The secondaries are controlled by a stop that limits how far they are allowed to open. This stop is controlled by vacuum.
When you start the car and let it idle the car produces (stock with no vacuum leaks) about 21 vacuum. This vacuum holds that stop in place. As you increase revs, the carb opens up more, letting more air flow in, vacuum starts to decrease, taking pressure off of the stop. When you go WOT, vacuum goes to 0 allowing the secondaries to now open.

Pop your hood, take off the air cleaner lid. Tap the throttle all the way to the floor and let off, you'll see them open slightly, about 1/2 inch on my 305 with a E4ME.

Good luck!

Well, here are a couple things that could go wrong. One, the choke doesn't open all the way so the lockout linkage won't clear the pin on the sec. throttle shaft (see pic) and two the throttel plates are sticking in the carb bore. The second one usually happen's on high miliage Q-jets. That happend to us at a 406 dyno session. We made all our runs with a 750 Holly but wanted to try the 750 Q-Jet to record the differance but never got the chance because the sec would not open !! Bummer. There is no stop for the sec throttel plates so when they close they hit the alum carb bores. As years go on they make a grove in the bores (hard to see) which will prevent the plates from opening. So, I made a stop (see pic) that holds the plates just barley open which allowed the plates to open the same all the time. Cars that drag race the dial-in sean really benafit because they make more consistant runs.

Auggie