by ron bennett » Fri Nov 20, 2009 12:54 pm
Oh, what the heck, I'll dive into this pool.
The only difference, for any given engine application, between a Perry non-pump carb and a Perry pump carb is that the pump version has a larger ID bore. With a pump on the engine, one does not need the venturi effect to draw a suction to pull fuel into the engine.
The bigger bore and higher fuel flow on a pump system with a pump carb gives an increase in torque across the power band and a very slight increase in HP from a slightly higer RPM.
It is all but impossible to have a smooth reliable idle, correct high speed needle setting AND a smooth mid-range transition with today's carbs with only a idle setting and a high speed needle setting. You could improve this with an in-flight mixture adjustment, but that would be a real pain to use.
The black slide barrel HP Gold Seal carb and the Webra Dynamix carbs are better than others at mid-range transition becasue they have assymetric barrel action, but are not ideal.
Ron Bennett
Hope this helps clearify.