Hi cracks!
I have a 1969 firebird 455ci engine with E-heads, cam, carburator, ignition, etc. etc.
If I do a kick-down it very often happens that it seems the car does not get enough gas. I have to lift the gas pedal for 2-3 seconds and then it speeds up again.
Is that a known problem about modified engines? Do I have to install a second gas pump?
Hope you understand what I am writing. Enlish is not my mother language.
Cheers from Switzerland Olivero

Welcome,
One fuel pump is enough if it works right. Do a test at idle and see how much gas your pump can pump into a container. A stock pump will pump a lot more fuel than you can burn unless you have a couple big carbs....

If you have a Quadrajet or other carb with the spring loaded secondary air valve, set the air valve adjustment. It may be opening too soon.

Some info on Q-jet's;

The accel pump lever has 2 holes. The inner gives a short shot.
The outer gives a longer shot.
Either may be correct depending on engine build.

Put a large inline filter between fuel pump and carb, and remove the one in the carb inlet.

The secondary "upper" air valve can be adjusted to open faster or slower(usually opens to fast).
There's a set screw on outer right rear(under the shaft) to adjust spring tension.
More tension slows the air flap opening.

Holley's have to many versions to give detailed advice.
But usually it's float level and pump shot adjustments.

Yellowbird beat me.
Had to wait on customers while typing.

But your answer was more thorough.

Hi all

Thank you very much for your answers.

I have a new JET Performance Carburator installed.
My Mechanican told me that the ignition is still not setup optimal. He wanted to have it like that until I drove another 600 miles. The Engine is completely new build up.
Even the gas pump is new. I just dont want to install another gas pump and it does not help.

Cheers,

Oliver

Your mechanic probably has your timing a tad retarded for break in. You will have the 'bog' until it gets advanced for full performance....

Sound like you're not getting enough fuel. Provided that your carb is set up correctly you might want to check your fuel pump. Make sure you have the correct pump...for a 455..not a 400 or 350. I had a 455 in my 67...the 455 used more than the stock 400 fuel pump could produce. I ended up with an electric pump, and larger fuel lines....problem solved.

Most likely you had a problem that whatever you did when you installed the electric pump fixed it. A stock v-8 mechanical pump will provide the fuel you need for a 455 with one carburetor up to, at least, 850 cfm.