Hi Guys,
I have a 1976 F-250 that I wanted to get a rebuilt carb for. The further I get into this it seems the more questions I have.
My VIN indicates that the motor in my truck is a 390. A valve cover sticker indicates it's a 360, and the D4TE on the engine block seems to indicate a 1974 330.
The casting number on my intake is C8TE 9425A which indicates a 1968 intake for the 360/390. The carb that is on it is an old school 2100. My carb has no tag and no numbers. National Carburetors identified (from pics) it as being from a 1970-1972 Ford Car (ND2369A). When I asked them what jets they sent with their carb they said 48's - mine are 54's. Venturi size is 1.23 stamped on my carb. No idea what their's is yet. Anyways my question is - is the 1.23 venturi with the 54F jets too big for my engine? It seemed to run fine before. Would the 48F jets be too small? I live at 909' foot elevation if that makes a difference. I just think going from a 54 to a 48 is drastic but maybe not? Any help would be appreciated. Thanks

 

Venturi size, and jetting gets complicated. Keep in mind though when a carburetor is jetted right you could install it on a completely different size engine and (within reason) would not need rejetting. 1.23" venturi is probably a bit on the large side. Small(er) carbs are better for "trucks that get used as trucks" hauling loads, or even just cruising around, trips to the yard waste site, hitting the DQ, etc. Venturi size and intake plenum are chosen by the OEM for high velocity and best atomization of the fuel. Choose a carburetor that best fits the intended purpose, for my money a smooth idle and crisp throttle response just off idle with good torque is best. I don't care about 6000+ RPMs or high speeds or racing stuff in a low compression stock Y-block for example. It shipped from factory with a 1.02" 2100, it runs well enough.

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