Sounds like maybe your accelerator pump(s) aren't working correctly. Does it do it only when you stomp on it, or will it still stumble if you bring it up slowly?

The accelerator pump is the part that squirts extra fuel in when you mash on the throttle. So if you're at the carb (without it running would be easier) work the throttle a couple times and see if you can see fuel squirting into the barrels.

Is the dying only when you stomp on it and then let off fast, or does it do it when you let off fast all the time?

 

The accelerator pump works very well. I can see it pumping fuel when I press the throttle.

It doesn't always stumble when flooring it, sometimes she's got a slight stumble (I'm wonderin if its my automatic choke, I'm gonna wire it open tomorrow), but even then she'll scream like a striped ape

It dies anytime you let off of it fast if the RPM's are above 3K (I'm guessing here). I don't know if it will still die if I don't stomp on the brakes.

I'm wanting to blame the the vacuum advance, and am going to take the dist apart tomorrow.

 

What carb is on this 307? I'm thinking Quadra-jet.

80's Q-jets were tuned for emissions, and not power. They almost ALWAYS stumbled when punched. They've got to be tweaked a little to keep from falling on their face.

What happens is that when you punch it, the manifold vacuum drops to zero almost instantly, and thus flow through the venturis stops. Your pump shot has to be big enough to cover that "hole" (and stock, it's not anywhere NEAR big enough) until the engine speed picks back up and starts the venturis flowing again.

Huge secondaries and numerically low gear ratios mean absolutely horrid off-the-line performance; but you can cruise at horribly illegal speeds for DAYS....

Some things to try:

move the accelerator pump rod to the OUTER hole
raising the float level about 1/16 of an inch
stiffening the spring on the secondaries so that they don't open QUITE so fast
snipping off 1-2 coils on the power-piston spring
finding main rods with a smaller taper diameter OR bigger jets

Tune your choke so that when it starts and the choke pull-off dashpot pulls the choke slightly open, it pulls it open ONLY enough to clear a 1/8-inch drill bit (regardless of what the manual might say).

This is just some stuff I remember off the top of my head, from trying to get a '79 Chevy truck with a 305 to run with a HYOOGE 800 CFM Q-jet. 10+ years ago.

(of course, if you're not running a Q-jet, then only the theory above applies. )

-blaine

 

Sorry, thanks for all the info blaine, but I tossed the Qjet over my shoulder for a Holley 650

 

Yeah you definatly want to wire the choke open. If not it can slam shut when you get hit. Causintg you to stall out. You also might want to slightly retard the timing. This helps later in the derby when the engine gets hot and you need to start it.