Stumbling when secondaries open

[280z turbo]

https://youtu.be/wyrLvc43xfE

I've got a 327 with an early (circa 1965) Quadrajet that is bogging badly under hard acceleration. It idles and revs just fine, but load it up and it stumbles as shown in the video.

The carb has been rebuilt and cleaned and I can confirm that it ran fine before I rebuilt the motor and installed a more aggressive cam. I would guess that it's making around 300 hp now and was probably making 200 hp before (it was in bad shape). I tried tightening up the spring tension in the secondary air flap. It helps a little bit, but I think it just masks the problem slightly.

The main jets are .071"
The primary metering rods are .045"
The secondary metering rods are AN .069" tip
The secondary hanger is an H

The engine seems to run fine on the primaries, but bogs on the secondaries. I am looking at CK metering rods 0.0527" diameter. Is this going to be rich for a 327 with a mild performance cam?

[Cliff Ruggles]

What is the carburetor number?

[280z turbo]

I don't know. The round tag fell off. I believe the carb came off of a '65 Impala 327 with 275hp and a Powerglide based on the numbers on the engine and manifold.

702xxxx

[Cliff Ruggles]

Can you put up some pics of the carb?

[280z turbo]

Can you put up some pics of the carb?

[73ss]

I don't see a choke pull-off in the pics. Do you have one on the carb? Is it any good? Would cause the problems you are having. I'm not certain but I think '65 327's still used the old 4G, or a holley on the hi-po models.

[Cliff Ruggles]

It's going to be a very early unit 1967 most likely.  They used the old bypass/plunger fuel valve set-up into 1967, but 1965 and 1966 models don't have the pull-off and link up to the secondary airflap shaft.

+2 on the link and pull-off, they MUST be in use, with correct release time and link correctly adjusted, or it can lead to a stumble when the secondaries come in.

Other players are the secondary plastic cam and spring.  ALWAYS replace both during a rebuild, all of our kits come with those parts.

Third item is the accelerator pump.  It provides fuel to not only cover a lean condition on the primary side, it helps the secondaries as well.  Hopefully you have one of our pumps in there and come with a custom seal that will not fail in this new fuel and custom wound springs for improved performance......Cliff

[280z turbo]

It's going to be a very early unit 1967 most likely.  They used the old bypass/plunger fuel valve set-up into 1967, but 1965 and 1966 models don't have the pull-off and link up to the secondary airflap shaft.

+2 on the link and pull-off, they MUST be in use, with correct release time and link correctly adjusted, or it can lead to a stumble when the secondaries come in.

Other players are the secondary plastic cam and spring.  ALWAYS replace both during a rebuild, all of our kits come with those parts.

Third item is the accelerator pump.  It provides fuel to not only cover a lean condition on the primary side, it helps the secondaries as well.  Hopefully you have one of our pumps in there and come with a custom seal that will not fail in this new fuel and custom wound springs for improved performance......Cliff

The choke pull off is brand new. These pictures don't show it. The accelerator pump seal is also new.

I replaced the cam and spring on the secondary flap in response to this problem. It still happens.

This setup worked well with the old cam and worn out motor, which is why I believe that it's related to calibration.

[Cliff Ruggles]

Did you get our pull-off and pump seal, or from someplace else?