Distributor vacuum advance

[Juan Veldez]

If I bypass the OSAC valve and the By-Pass valve, where should I plug the vacuum advance hose to on a Thermoquad? Or does it connect to the vacuum tree at the back of the intake? This is a 73 Chally with a 340.

 

[Jm73340]

There is a ported vacuum port on the front of the carb. It is a small port and should not have any vacuum at idle.

 

[Juan Veldez]

There is a ported vacuum port on the front of the carb. It is a small port and should not have any vacuum at idle.

These are three ports on the front of my carb. Large one is for the crankcase pvc. The small one below it and towards the driver side is for the charcoal canister purge. And the one towards the passenger side up high in the black plastic is for the egr venturi vacuum (not currently used). The two in the back are for the choke and the air cleaner vacuum. The manual shows another port on the front of the carb for distributor advance, but my carb does not have that - see photos. Also, what is that port up high on the front that has a plate with three screws holding it in place? My carb must not be from a 73 small block as it does not look like what is in the manual - ugh.

 

[Jm73340]

Picture below is from my 73 service manual.

 

[Juan Veldez]

Picture below is from my 73 service manual.

View attachment 97064

I got the same 73 manual. The OSAC valve fitting (distributor) port is not on my carb. Mine might be an older carb? I figure it should connect where there is little to no vacuum at idle and then increases when you increase rpms. Just don;t know which port(s) that may be.

 

[72RoadRunnerGTX]

These are three ports on the front of my carb. Large one is for the crankcase pvc. The small one below it and towards the driver side is for the charcoal canister purge. And the one towards the passenger side up high in the black plastic is for the egr venturi vacuum (not currently used). The two in the back are for the choke and the air cleaner vacuum. The manual shows another port on the front of the carb for distributor advance, but my carb does not have that - see photos. Also, what is that port up high on the front that has a plate with three screws holding it in place? My carb must not be from a 73 small block as it does not look like what is in the manual - ugh.

Clearly a later Thermoquad, likely a Lean-burn carb. Does not have a dedicated vacuum advance port. Get the carb number off the driver’s side rear mounting flange, will tell you just what the original application was.