motorcraft 4300 carb info

[Jeff Lee]

To clarify, the 4300 Autolite is different from the 4300D Autolite in that the D series is a spreadbore with larger throttle blades than the 4300 "non D", correct? I believe the 4300D was rated at about 715CFM. Correct me if you have other info (I run the 4300 non-spreadbore).
And I probably should not reference this as a "spread-bore". Square flange or spread-bore flange may be more accurate.

[FED 387]

According to a buddy of mine these are the specs for both carbs

4300 Carb depending on the particular model these measurements can vary from

441-605 CFM
Venturi 1-1 1/4 in primary

Bore 1 7/16 P--- 1 9/16 S
1 9/16 P-- -1 11/16 S


4300D carb

715 CFM
Venturi 1 1/4 P
Bore 1 9/16 P--2 S

This carb (4300D) is ONLY on 71 Boss 351 Cleveland & 72-74 351 Cleveland engines ---4300D carb will only fit a specific manifold -- Not interchangable with a 4300 manifold WITHOUT an adapter!!!

Comp 387

[gmonde]

jeff we do run a spread bore (not much of one ) but it is a square flange bolt pattern
1 9/16 P-- -1 11/16 S and a 605 cfm "man talk about a choke " gmonde

[FED 387]

605 CFM carb came on the 1971 351 cleveland engines NOT the BOSS engines those were 4300D==Comp387

[dwydendorf]

The motorcraft and autolite carb with the square (not spreadbore ) baseplate is refered to as the 4300A. As far as I know there were basically two sizes of these carbs, a smaller version that came on the 68 302 and 69 351w engines and the bigger version that came on the 70-71 351c and 68-75 429-460's. I also heard that the AMC's had some of these carbs on their engines. I ran one on my 70 mustang in SS and it is very touchy carb to mess with, a real pain.

[FED 387]

4300 carbs were rated @
441 cfm--67-68 J code engine
470 cfm -69 351W
595 cfm-69 390 S code engine
600 cfm-70 351 W & 351 C engine
605 cfm-71 351 C engine
715 cfm 71 Boss 351 C & 72-74 351 C engines--THIS IS THE 4300D CARB

[Jeff Lee]

The AMC 360-390-401 of 1970 thru 1972 (390 was discontinued with the introduction of the 401) used the square flange (Holley, Carter, etc., interchange) with the 1 9/16" x 1 11/16" throttle blade size as correctly mentioned by Garrett. After 1972 AMC used the spread-bore flange on the 360-401 which was also used on the FOMOCO 429-460 engines.
I've found the 4300 to be a decent carb with the exception of the bowl size and of course CFM. Although not as bad as a Q-Jet fuel bowl I suppose. I've found it is well engineered as BSFC numbers are pretty decent with just jetting changes (there are no secondary jetting or metering rods). In fact, when we started playing with air bleed sizes, minute changes +/- from stock just killed power. And the fuel bowl wasn't an issue untill I started running Superstock and that problem was also corrected. But it definetly is not of sufficient CFM for a 390 engine!
Now if only we could get those pesky 351 Boss and Clevlands to also run the factory supplied carb, we would really see who was on top of their game!

[Jeff Lee]

Originally Posted by FED 387

4300 carbs were rated @
441 cfm--67-68 J code engine
470 cfm -69 351W
595 cfm-69 390 S code engine
600 cfm-70 351 W & 351 C engine
605 cfm-71 351 C engine
715 cfm 71 Boss 351 C & 72-74 351 C engines--THIS IS THE 4300D CARB

715 cfm 71 Boss 351 C & 72-74 351 C engines--THIS IS THE 4300D CARB
And you should have mentioned VERY EXPENSIVE CARB! (as in gold plated category)!