V4 100HP 1972 Carb Inlet Question

[wireready]

I'm removing my high speed inlet screws to clean them out. I have the service manual and it has nice diagrams, but I'm puzzled... the high speed inlet screws are inside a channel, in front of the drain plugs. How exactly do the fixed high speed inlet screws work in that kind of carb. Most carbs use needles, and I understand how needles are used to restrict passages that gas flow through, but in the case of the fixed inlet screws which are just a round hole, how does this regulate the flow of gas. I've never popped the core plugs out (which might answer my question) but I'd love to see a diagram or have anyone explain the course the fuel flows through the carb with respect to the high speed fixed inlet screw/orifices,

i.e from the pump down the fuel tubing through the needle valve... where it fills up the float chamber. how does it then go from there, into the throat during high speed and how does that high speed inlet screw play a roll, I can't see how the fuel would travel from the float chamber, into that inlet screw where it's orifice would do anything. I see how the low speed path works through the low speed orifice, but the high speed route for gas puzzles me.

Does the gas actually travel through that channel, and it has to go through the inside of the inlet screw in order to make it's way up into the throat of the carb?

 

[Joe Reeves]

Re: V4 100HP 1972 Carb Inlet Question

An adjustable high speed needle valve does not close off the passage altogether obviously, and I know you understand that. This leave a space around the needle valve point that fuel flows by that could be calibrated into a certain amount of space for the fuel flow.

This is exactly what has been done by doing away with the adjustable needle valve and calibrating that amount of space into one inside diameter hole within the brass high speed jet.

Fuel must flow thru that high speed jet before it can obtain passage to any other fuel passageway. At the high rpms, the throttle butterflies open and create a strong vacuum across the top of the brass high speed nozzle. This causes the fuel to be drawn thru the high speed jets and up the high speed nozzle and then into the carburetor throat, intake manifold, etc. A very simple and efficent operation.