HIPO Carburetors

My understanding. The C4OF-AL was introduced approximately mid-May 1964 into new engines at the Cleveland Ohio plant for cars with PCV systems and manual transmissions: 1964 Fairlanes, 1965 A.C. Cobras, and 1965 Mustangs. All HP289 engines made through July 11, 1964 were 1964 model year five bolt bell housing ones no matter what car models or model years they went into.

The C4OF-AL carburetor model carried over into the 1965 model year PCV vented engines and vehicles with manual transmissions.

For the 1965 model year Ford installed road draft tube systems for some engines for locations where PCV systems were not required. The C5OF-L carburetor model was created for those engines and cars. The functional specifications C4OF-AL and C5OF-L models were almost the same. The differences was all in fuel jets. C4OF-AL for use with PCV system used 51F and 70F jets. C5OF-L used with road draft system used 52F and 68F jets.

The most believed theory is that 1) Ford made large quantities of C4OF-AL models for new cars and over-the-counter sales as they were recommended as a post new car retail sale enhancement for all kinds of engines and cars street and race from 260 c.i.d. engines in Sunbeam Tigers to 427 c.i.d. engines in sedans, and 2) when a batch of carburetors were required for 1965 for road draft tube vented engines, for sale in states that did not require PCV systems, some C4OF-AL models in progress were finished to C5OF-L specifications and tagged as C5OF-L models; body stamped C4OF-AL and assembly tagged as C5OF-L.

Changing specifications is as easy as changing jets and no telling how many carburetors tagged a C4OF-AL got converted with a change of jets to go with a nice C5OF-L tag somebody came across. That said, the common conversion has been to find a new car take off C5OF-L, remove the C5OF-L tag, rejet to C4OF-AL configuration, and put a C4OF-AL tag on the keeper carburetor. I have seen quite a few done that way. Of course some tags out in the world are reproductions now.

Bob Mannel's publications indicated that 1965 model year road draft tube use ended March 1965.

Fred may have some better information.

There were more than a dozen new engine assembly line HP289 specific carburetor models listed in Bob Mannel's book for the 1963-67 model years. Then there were revisions within HP289 model families and there were service replacement HP289 models not exactly like in looks or function covering 1963-67 model years. Ford 4100-A carburetors as a general subject is much more complicated than most seem to be aware of. Ford engineers did the work to develop carburetor specifications to fit exact new car applications.