[Jac Mac]

Originally Posted by Gaz64

I've been a mechanic for 33 years, I don't have an "engine builder" since I do all my own.

I never said it was right or wrong either, I gave my opinion of what it could be in post 16, then you chime in at post 24 with "your info" which would make no difference to the carb idle speed.

I have never seen this done to ANY carb, it makes absolutely no sense to drill holes in the barrel after the venturi to allow unfiltered air into the engine.
To me it wouldn't make a scrap of difference to how the engine runs from idle to high rpm.

As another member has stated, atmospheric pressure would be on both sides or very near to it.

Gary, you should have started 10 years earlier.
Most if not all of the carbs fitted to 6 & 8 cyl Holdens, Chrysler Valiants, and Ford falcons produced in OZ during the 1970's & earlier have similar holes drilled above the throttle plate area. In this particular case with the standard production carbs/engines it was to help prevent fuel pullover from the main venturi when the choke was in operation with the throttle blade in the fast idle position. Strombergs, Carters & Email? carbs, both single & 2bbl had this feature, I will have to have a look at some Autolite/Motorcraft carbs to check, but I think some of them had an internal drilling/passage from above the choke horn to the throttle plate area that performs the same function, plus uses cleaned air. You have to remember that in this instance the carb airflow ratings and venturis were quite small .