Jerry - this is the reply to your PM.
First - I have never seen these modifications to a Rochester B, so cannot give you a definitive answer.
Having said that, historically:
(1) Various companies have provided throttle plates with holes of varying sizes since the 1930's for at least two different reasons:
(A) As an idle air bypass. The fuel provided by the idle circuit is proportional to the air velocity of air passing the idle discharge hole in the throttle body. If the air volume required at idle is sufficiently large (huge camshaft, or large displacement engine) to cause the throttle plate to be open further than the optimal opening for maximizing the air velocity, idle quality will suffer. The hole in the throttle plate allows a certain amount of idle air to flow through the hole, allowing the throttle plate to be adjusted such that the velocity of air flowing past the plate is maximized, thus creating sufficient negative pressure in the idle circuit to allow sufficient fuel to flow. This picture may help with the understanding of air velocity:
[img]
http://www.thecarburetorshop.com/Carter_multiple_venturi.jpg[/img]
This is the main venturi, but the same principal applies. This was a lab exercise in the Carter Carburetor School. One can see the glasses of water, and the water head drawn by the negative pressures at different points. Fuel flow is dependent upon air velocity!
(B) Pontiac provided throttle plates with very small holes on the end carbs of some of the tripower setups. The purpose was to allow a tiny amount of fuel to bleed through the end carbs, keeping fresh fuel in the carbs.
(2) Opening the idle discharge hole is a performance only modification or an attempt to make a totally wrong carb work on an engine. Not saying it is never necessary, but in 60 years of working on carburetors, I have personally never had to do this; have always found a better way.
(3) The long needles have been tried with the extension used as a deflector to break up the air stream; generally on vehicles designed for low end torque, and low maximum RPM.
In the "for what its worth" category, if I saw modifications like this on any carburetor, I would assume other modifications had been made; and, unless this were a Duesenberg carburetor or a Ram Air IV Pontiac carburetor, or others in this range of difficulty to locate and value, I would scrap it and start with a different core. If the carb is Duesenberg or the RAIV Pontiac where the customer is independently wealthy, and can afford the labor, I would totally strip the carburetor and compare each component against the original manufacturer's blueprints. This a a VERY time-intensive process.
Jon.
