Carb Adjustment Question - '29 Plymouth

[racertb]

Other than the screw seems a little loose, it screws in fine to the carb.  When screwed in all the way, it's tight.  Right now, I only have it back out of the card about 1/2 a turn; air/hissing sound still there, but obviously quieter.

[plym_46]

threads on the screw look decent hoe about in the carb?

[racertb]

Here's the spring and screw:

[racertb]

Thanks...I will look at the butterfly to see if it properly seats.  The screw does make a difference when screwing it all the way in or all the way out.  It just seems like there is too much "play" with it as if it's worn...

[plym_46]

Nope shouldn't be any air flow there.  If it,s is sucking air it's way two far out or the threads are bunged up.  Screw it in till it lightly seats, then turn it back out 1 1/2 turns,  If it needs more than 1/2 more turn in either direction to get a good idle than something else is wrong.  Since the screw only effects air going through and mixing with gas in the idle circuit, no amount of adjustment will make any difference if the throttle is not closed completely against its stops.  The fuel feed through the idle circuit is constant at any given RPM with the throttle closed and the screw only regulates the air that mixes with it.  If the throttle is not completely closed the screw can not make a large enough adjustment to deal with that amount of air bypassing the butterfly.  Also if there is an air leak between the carb and the manifold on either side of the gasket or if the line to the fuel pump is leacing vacuum, that will ass to the problem. Take an unlit propae tourch cracked open a bit and direct it worards the screw the bottom of the carb, the trottle butterfly pivot bushings, the carb base, and where the intake manifold joins the head.  If the engine speeds up at any of these places it means its sucking air, wen it picks up the propane, it will richen the mix and speed or smooth the idle.   Before you figgle with the idle screw setting make sure you don't have any leaks in these areas.

[racertb]

All:

I was working on the car today and "playing" with the idle control screw/fuel-air mixture screw (#5 in the instruction book) and noticed that while fine tuning to what I though was a good setting, there seemed to be a "hissing" sound (air) coming from that part.  That is, I could place my fingers on the screw itself which would stop the hissing/air, as if the screw was loose inside the housing.

My first thought was/is this is not normal and there shouldn't be any leak/suction (air) here.  Am I correct in this?  If so, is the screw somehow worn out causing excessive play?

Has anyone had this issue before or is this normal operation?

Thanks,

Ted