Hey guys, newbie here, i have a late year 1970 270hp 350 with a early year 71 engine and q-jet (original from factory) 40 some thousand miles, car was sitting for 20 years, started up every few years, i am in the process of restoring her and am running into a bad accelerator pump leak. i had the carb rebuilt last fall by a carb guy, ( will be calling him later today but wanted to pass this by some vette guys too) she will start up fine and high idle at 1000 rpm with no leak but after she iswarm and you give her a rev or too to get off of high idle she will stumble around 4-500 rpm and leak like a sive aroundthe plunger for the acc pump. ihave had her running good last fall and set the idle then around 700 rpm. realy havent put any miles on the rebuilt carb, some things to note are:

The only way fuel can be around the top of the pump plunger is if the fuel level is too high.  It sounds like your needle and seat are leaking again.  Either you didn't get a good quality one before, or there is junk in your fuel system that gets in the seat.

Larry

I agree with Larry...the fuel level is too high. At higher idle/engine speed, the engine can handle the extra fuel, but not at normal idle. As Larry says, the only way for fuel to run out thru the acc. pump hole is for it to be too high to start with.
So....either the float is sticking, or not set properly, or there is some trash in the needle/seat assy that is not allowing the needle to fully seat, and shut off the fuel flow.
Whatever the problem is, it is definitely inside the carb, from the description.

btw...Welcome to C3VR!!!Adams' Apple2009-04-14 10:02:47

Yep, too high of a fuel level.  But the float may not be floating, or the needle and seat may not be seating.

Well, the SOB carb builder isnt returning my phone calls, so i may have to tear into this myself. Would too high fuel pressure cause this problem too? i remember seeing something like this being the cause on one of my eldebrock 1406 installation dvd's. Also, how would i test the fuel pressure? i have a vaccum/presure testor, do i simply hook this up to a T fitting in the fuel line from the carb to the pump and start the car?

Stock needle valves can't hold more than about five pounds pressure, but there is no need to run more than that.  If you have an aftermarket fuel pump with more pressure than that, unless you are making 500 HP and need the volume, put in the correct pump.  A work-around would be to put in a fuel pressure regulator.

Larry

Wow really? 5 psi, my chiltons manual says that the carb needs pressure of 7.5 to 9 psi. this sounded kinda high to me. i bought a stock replacement pump from Napa last year, maybe it is pumping out too much psi. Anyone know how to test the pressure using a gauge?

Just disconnect the line from the carb, and attach the pressure gauge to the line.  Crank the engine, or start it, and read the pressure.

tested it last night, i am getting a fluctuation in the 3-5 psi. range, should i be worried about the lower range of this fluctuation (i.e. the 3-4 psi)? well the leak from the accelerator pump is a lot less this time around, but it still leaks. i noticed another leak when i turned the car off, it looked like it was coming from the gasket or a mixture screw in the base plate in the area right under the acc. pump. i have the original heat insulator? under the carb right now (intake, gasket, aluminum plate , gasket, aluminum plate, gasket, carb) i may try just throwing on one of the single thick gaskets between the intake and carb to rule out a gasket leak. i am worried that all those gaskets and plates may not be creating a good seal. thanks for all the help guys, carb diagnostics and work are still pretty new to me.