Idle adjustment bypass air?

[raf2330]

Hi. Looking for input on how to get idle correct. Engine is 454 in a 73' C20. Primary's are adjusted high with idle screw right now and I have no control with idle air screws. Right now idle is at 800 RPM. Timing 12, manifold VAC. Shaft bushings have been installed. Vac hole from choke blocked.

Carb #17084502
Idle air screw holes: .093
Lower idle air bleeds (main casting):  .062
Upper idle air bleeds (main casting):  .070
Bypass air in baseplate at primary's:  .110
Air bleed in airhorn:  .070
Upper idle air tube: .050
Lower idle air tube: .040
Transfer collar:  .045
Primary jets: 73
Primary rods: 49M
Secondary rods:  ED
Cam: 110 LS, 224/230,  .515/.520
Compression: Not known, I didn't build it. Trying to get with builder.
Heads: Chevy CI 078
Turbo 400 trans
3.73 rear end
vac at idle 13hg

I did some tuning several years ago on one of these with somewhat of the same condition. Had to add bypass air. I think that is the case here, I'm just not sure where to start as the existing bypass #'s seem all over the place.  Maybe I'm wrong, just not sure. This cam is very different from what I dealt with before also. Any help is appreciated.

Thanks,

Ron

[Kenth]

I guess you are reffering to the idle mixture screws when you write idle air screws?

But i can´t figure out what these are:
Upper idle air tube: .050
Lower idle air tube: .040
Transfer collar:  .045

Also, did you pull the idle tubes for measurement? Their size is critical for proper idling.
And most 1974 and earlier 4M Chevy Quadrajets with BB engines uses about .138" idle bypass air, some 1974 units .170". Later M4 units uses about .110".

[raf2330]

Yes on mixture screws.

I guess it should be idle air tube .050 & down channel .045.
There is a brass insert next to the idle air tube/down channel that is .045.?
I did not pull, I used assorted # bits to size. I will pull if necessary.

It seems from your comment that all the by pass air may need to be min .110 to start?

Thanks for your help sir.