7042263 has surge on light throttle

[liberator]

Just did a rebuild on stock 7042263 on 72 GTO with 4 speed. Starts up great with good cold start and choke works well. Idles great and has good acceleration, but has surge or slight stumble at light constant throttle.  Engine is stock 400 with no mods, at idle vacuum is around 18 and timing is set to stock.  Plugs are burning a somewhat white in color.  Jets are stock 72's and metering rods are also stock 45's.  Stumble seems to smooth out if I manually close choke butterflies a little while I hold throttle open around 1500 to 1800 rpms.  Thinking it is running lean, so I just ordered a set of your power piston assortment springs to perhaps increase the piston open pressure to keep the metering rods higher in the jets.  I was wondering which of the assortment springs would be the best to try first over the stock spring.  Thanks, Dennis

[Cliff Ruggles]

Did it do this before you "rebuilt" it?

Did you use one of our kits?

The PP springs will NOT help that issue, as there is PLENTY of vacuum at light part throttle that with any spring being used the PP will be in the down position.....Cliff

[liberator]

When I bought the car, it had not run in several years and carb was pretty dirty and I did not drive the car before I rebuilt it, but it did have a bad bog.  I had a kit for the carb on my shelf, and basically the rebuild consisted of taking carb apart, cleaning it and adding a new float, & accelerator pump and gaskets and fuel filter.  I have put in new plugs, wires, cap, rotor.  Like before it starts up fine, choke sets well, kicks down when warm and idles great. WOT appears to be good, but just has the surge/miss at low to mid throttle which seems to diminish when I manually throttle it while closing the choke flap by hand.

[liberator]

I had a another quadrajet sitting on the shelf that I had from a couple of years ago, a 7043250 carb that I believe is for a 73 olds 350, that I took it apart, cleaned it and put it back together, retaining all original jets, metering rods and even accelerator pump.  Put it on the GTO, and it eliminated the mid RPM surge or hesitation. It actually runs pretty good with that old carb.  So now I know my original carb is the issue.  Any idea what might be causing this mid range rpm surge and hesitation with the original carb?  That is why I was thinking is was with the PP being drawn down with a weak spring.  Castings on the original carb looked very good, with good original coloring and lack of any corrosion, also looks to have never been rebuilt before.

[Cliff Ruggles]

It is running lean, the power piston spring used will not help that issue.

If you installed the needle/seat assembly from your parts kit it will be the wrong size, so fuel level will be lower and add to the issues of being lean.

That carb requires the .135" fuel inlet seat.

I would also install a smaller metering rods while it's apart, and absolutely and for sure install one of our accl pumps in it while the top is off.....Cliff