[UngerMarkus]

I put duct tape over the air valves and the hanger to prevent them from opening.

I did what you said and checked the PP with a screwdriver. It seems to work smoothely.

As for the casting number, I´m gonna check that and let you know. As far as I know it´s a brand new Jet Carb set up for Smallblock Truck engines.

[raguza123]

Ok you do know the secondaries still open, even when you tape the air valve off?

[RWENUTS]

How many turns on the screw are you at on the secondary air valve. Measured from zero adjustment. I tap on the air valve and when it won't try to close I call that zero.

[UngerMarkus]

Thanks for your replies, guys!

I did what you suggested me and checked the PP with a screwdriver. It works nicely.
Unfortunately I forgot to write down the casting number. But it is a Jet performance light truck stage1 carb.

The APT was screwed out 4 turns. I tried everything from completely seated to 5 turns out in 1/4 turn increment. But it didn't make much difference. I also advanced the ignition a bit.

In D it drives badly. When I locked it in first gear it accelerates good as long as you open the throttle progressively.
When I floor it, it stutters badly and does not pick up speed. When you let off the gas a bit, it accelerates again.

[UngerMarkus]

From the point where the spring doesn't close the air valve anymore I loaded the spring with one full turn.

[RWENUTS]

Getting stumped!!
Blow some carb cleaner thru the air bleeds that are located between the choke housing and the secondary air valve. In photo 2 in the link you see them 4 tubes that are attached to the top plate. Best to remove the top plate to check they're clear. I found one once that was pinched off.
You could try blowing thru them without lifting the lid.
Diagnostic Dilemmas: Servicing Quadrajet Carburetors: Underhood Service