carb lays down under full throttle

[454scotty454]

hi all,
    I have a carb problem. When I floor the carb, car pulls hard up until the tranny shifts then the rpms go down to 2500 and stay there unless I let up on the gas. I can hear the exhaust popping. The car runs well at idle and light part throttle.
I have read it could be fuel delivery. I bought a new mechanical pump from GM and it was DOA. Put the old pump back in until I can exchange it for a new one.
Car 1988 caprice stock 350 all emissions exist and working original ccc q-jet.
Should I convert to electric in-tank pump like the GMPP 350 camaro conversion kit does or get an aftermarket mechanical pump?
Thanks for any and all help

[Cliff Ruggles]

A good mechanical pump should keep up with that engine.

Has the carburetor been "rebuilt"?

Over the counter kits come with the wrong fuel inlet seat.  If the fuel inlet seat is too small, it can act like a fuel delivery problem.....Cliff

[454scotty454]

Cliff,
   Thanks for the reply. Carb is original as far as I know. The numbers match the year and make of the car. Id have to check the fuel inlet seat. What size inlet would you recommend? Car is totally stock except for headers and duel exhaust.

Have you heard of the fuel pump eccentric wearing down creating this problem? Engine has almost 200K on the clock. Pulls a nice steady 22 inches of vacuum at idle.

If I have to pull it apart I'm going to need a kit from you. I'm sure you have kits for the CCC q-jet? I can't send it in as the car is a daily driver.

What is a good mechanical pump? I figured the stock GM pump should be good enough for a stock car.

Thanks,
Scott

[Cliff Ruggles]

Our kits can be ordered with any size needle/seat assembly at no additonal cost.  The .135" should be plenty for your application.  I stock pump in good working order should also be plenty of fuel pump....Cliff

[454scotty454]

The fuel pump pushrod was 1/2 shorter than stock, so I replaced it. I ended up pulling the carb apart. Checked the needle and seat size, it was .120, too small! I installed a .135 from Cliff and have no more sag at full throttle. Still using the GM mechanical pump and not the electric intank conversion I was considering.

People check that needle and seat, it makes a big difference.
Thanks Cliff!