do some carbs use vacuum to cool the choke

on the passenger side of the carb is the choke assembly and coming out the bottom of it is a threaded port that sucks air all the time. i have heard this is for cooling this type of choke is this true or should i plug it off? the carb is a rochchester 2 barrel,(model 2g i believe)

 

cold/cooler ambient air is the only factor that contracts the bi-metal spring inside the housing; the housing is adjustable for desired operation.
the port you speak of is for warm/heated air coming off the manifold; this warm air helps in heating the spring while driving/engine running thus relaxing the choke and allowing the choke to open. Since warm air/heat rises I would doubt vac would be needed. Do you actually feel vac at the port ?

Some carbs do have a vac assisted device called a choke pull-off. This device uses engine vac to hold open the choke after engine warm up; it is used in conjunction with the auto choke spring housing.
I think Jeepster models used both of these on the Roch 2Gs, especially auot trans models.

 

What he said

 

Mine has vacuum there. If it didn't the heat wouldn't ever get all the way up to the carb to open the choke.

 

yes there is vacuum there all the time. my concern was if that vacuum would pull dirt/dust into the motor.

 

The routing on the 351M in my M715 was from the air cleaner, through a tube (part of which is coiled just inside the manifold on top) and then to the carb. This way it gets clean air from the carb which is warmed in the manifold and once warm helps to open the choke sooner. This is to improve emissions a little. I had so much trouble with the automatic choke on 2 previous carbs that I installed a new Holley 2-barrel with manual choke. No more choke problems.

Stan