Dieseling

[quadrajam]

My point with the distributor was that I was willing to to try anything at that point.
The distributor had nothing to do with it.

Sounds like your on the right track.

QJ

[68rs/ss]

Watching this tread with interest as I am having the same issue. Nervous to increase by-pass air any more to the point where I went too big. At .116" already. How large should one go before looking elsewhere in idle calibration? Such as in the idle air bleeds or idle tube restriction size?

[Kenth]

7040203 and 7045213 has the same specs, .092" upper idle air bleeds, .063" lower idle airbleeds, .039" idle tubes and .051" idle down channels.

I would start with this recipe for your carb on your engine.

[Chevynation]

7040203 and 7045213 has the same specs, .092" upper idle air bleeds, .063" lower idle airbleeds, .039" idle tubes and .051" idle down channels.

I would start with this recipe for your carb on your engine.

Thanks Kenth. I’ll be sure to check the idle bypass air hole size when I take the carb off tomorrow. The carb is great everywhere else and Cliff really was spot on with the recipe he put in so I don’t want to mess with it. I’ll just spec it out and do one change at a time. Idle bypass air increase by .010 should hopefully cure it depending on the current size. I’ll keep you posted tomorrow. Thanks.

[Chevynation]

.063 Idle fuel tubes and 0.196 idle bypass air. Took the carb off without touching the curb idle screw and the transition slot didn’t look bad. It must have been getting too much air because that slot exposure is with the idle screw backed all the way out. Im not too familiar with quadrajet but should there be transfer slot exposure with the throttle blades closed? I know holleys you can close the blades and have zero exposure. I shaved some of the gasket off to fix the manifold port on the carb because it was just blocking the hole. I was shocked to see how big the bypass holes in the base plate were. Correct me if I’m wrong but I traced the idle bypass holes from the main body down to these two holes on the baseplate and they’re a good size. I went to touch the secondary air flap and the tension spring broke. Good thing it broke now instead of on the car. Pretty weird but no big deal. I’m thinking that I go down .010 instead of up on idle bypass air but I would like an answer regarding the slot exposure with the blades shut. Any opinions?

https://ibb.co/7ndt1HP
https://ibb.co/VCLp3gy

[Chevynation]

The bypass holes are already pretty big it appears. If my idle screw was backed out that far and it was still idling at 750 then I would say I have too much bypass air and it’s running on from that and not the transfer slot which I thought before I removed the carb. Doesn’t anyone know the amount of transfer slot exposure for a quadrajet? Throttle blades are 90 degrees at WOT and fully close no light can be seen. The stop that’s on the primary shaft that the idle screw makes contact with looks like it should make contact with the main body for a stop but I’m coming up a little short. Not sure if this is a big deal or not but just something I noticed.

[Kenth]

I think you are measuring the idle tubes in the upper end? The restriction is in the lower end.
As for the off-idle slots they are exposed some in some units adding some idle mixture, use the idle needles to adjust the amount of idle mixture.
And the idle bypass air restriction is measured from underneath on the plate.

[77cruiser]

I've always seen more transfer slot on a Qjet vs. Holley, & it seems the later ones have more yet.
What you're showing for transfer slot is pretty good IMO.

[Chevynation]

It looks like the base plate idle air holes moved in 73 and my main body is a 75. So really my idle air holes between the body and base plate are misaligned. I looked at the carb and it looks like the gasket has enough of an opening to allow air to still allow it to work. Just thought I’d share that. I’m measuring the idle bypass holes on the bottom now. I looked at another quadrajet and there will be transfer slot exposure with the blades closed so that’s fine.

[Chevynation]

0.136 Idle bypass air. I’m not positive but the hose on my choke pull off valve was loose and I put my vacuum gauge in it while on the choke pull off and it wasn’t holding. Tried a different hose and it worked fine. I’ll put it back together as is to see if that was a vacuum leak.

[Kenth]

Use the correct throttle body gasket and your idle bypass air will be fine. Wrong gasket will block the hole on passenger side on your throttle plate.

[Chevynation]

Use the correct throttle body gasket and your idle bypass air will be fine. Wrong gasket will block the hole on passenger side on your throttle plate.

I currently have the 7038396. That’s why I had to shave some of the gasket so my manifold vacuum port would work.

[Kenth]

You are using the correct gasket for your plate, no "shaving" should be needed.
Pictures of your shaving?

[Chevynation]

You are using the correct gasket for your plate, no "shaving" should be needed.
Pictures of your shaving?

The holes were completely covered before I trimmed. I cleaned the gasket up a little bit so it didn’t look as ragged.

[Chevynation]

Found an issue. I’m only measuring 3” vacuum at the manifold vacuum port on the carb but I’m getting 10” at the choke pull off port on the carb. I pulled the tube out of the side of the carb for the manifold vacuum and it’s not blocked or anything. Before I shaved the gasket it wasn’t getting anything because it was blocked but now it’s so low that even my aftermarket vacuum advance can can’t add timing at idle. It’s not a straight shot down through the gasket from the main body bypass holes to the base plate. There is a recess in the base plate or main body I can’t remember which and the bypass holes are offset because the main body is in a different location than the baseplate due to the year difference but since there is a recess air should still get by I would have thought. I could easily blow air through the manifold vacuum port now whereas before I could not. Not sure what I could do to be able to use vacuum advance besides using a tee fitting at the choke pull off.