This will be ongoing, as I discover and reveal all of the inner workings of these... as well as what is totally jacked up about them in my opinion, inconsistent, unnecessary in my opinion, modifiable to be much better functioning in my opinion, etc... and thorough means completely opening things up, pulling back all the veils of previously secret/hidden calibration details and the sizes of everything, and what all those sizes of everything means, what can and should be changed, or not changed, what was previously thought not possible to do or revert back to traditional modular Holley function, parts-wise, but is/are entirely possible with some simple, minor modifications, etc.

The patient currently on deck is an original 1985 Mustang Holley/Motorcraft four barrel that I own, that I acquired on part trade for '72 R-code ( 4-speed, 3.91 rear gears ) maCh1 Mustang 351C HO's Motorcraft 4300C (previously also thought too troublesome and not worth bothering with, and runs like a champion now) carburetor and distributor work, that has a busted base plate, but most all else is there and fully examine-able...









Some of the calibration restrictions and bleeds, and where they are located:

IFR's (idle feed restrictions)...




The following are actually up-channel restrictions, since idle/transition air:fuel travels up these idle wells at this point within the metering block...




The following are final restrictions (at the bottom surface of the main body) to, the tailoring of exactly how much primary idle/transition air:fuel is allowed to be delivered to the primary transfer slots and the primary idle mixture screws... transfer slot restrictions in traditional Holley carburetors are not usually necessary to dial back transition fueling with stock or mild camshaft-ed engines... no worries, this is only one of a number of unnecessary calibration design aspects I have found within these carburetors original designed and meant for very stock/mild 302 engines...





For now, in closing, I'll just show my findings so far, and expand upon and discuss further later...






Any questions, comments, additions, please fire away...

Mike