motorcraft 4300 carb info

[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)!

[Tom Goldman]

The biggest issue with this carb other than it's relativly poor flow numbers, and the availability of decent cores, is the accelerator pump opperation . ...While this isn't an issue with a clutch or transbrake , it played hell with my car while I tried to run on the foot brake. .......I really could not count on a consistant launch or 60' time untill I gave up and went on the chip for the launch. .....Other issues are proper spring tension for the secondary air valve and making sure it does not stick. ....The acc pump hesitation and air valve were issues on these carbs from new, I've been working on them at the dealership since the mid 70's, and have a lot of service bulletens pertaining to driveability issues. .........Jeffs experiance with air bleeds may be unique to his "altitude" location....I've found the secondary air bleeds to be responsive to changes, particulary when we get the mineshaft air conditions. .........The secondary fuel passages definitly need attention,as they are small in relation to the metering tube. ........Definitly use only the large, single needle and seat. ....Do not use the secondary needle and seat as it will cause flooding when running over 3 or 4 psi. ..........I also dont use the power valve, but use a jet in its place. this will only work using a revlimiter on the launch........ Good luck, it only took me 4 years of playing with this carb to get the car to go 1.00 under. ...When I put on a Holley 650 out of frustration , when I built the car several years ago, the car immediately ran better than 1.10 under.......There is no easy road whith this combo. ........Tom

[gmonde]

i want to thank all who have gave there advise and comments,all of the info has nailed down alot of unanswered questions that i had,time to tinker gmonde

[SSDiv6]

Originally Posted by gmonde

i want to thank all who have gave there advise and comments,all of the info has nailed down alot of unanswered questions that i had,time to tinker gmonde

Talk to Dean Oliver: http://www.deanoscarbs.com/

[Jeff Lee]

Good advice from Tom here. Tom & I have spoken of these issues in the past and it would appear there are more than one advantage to running a stick car! I have attempted in the past to have the "known" carb builders tae on the challenge of building an Autolite for me and none wanted the work, including Oliver (but maybe he has changed his mind?). One that I received from an un-named "expert" was never tried previous to shipping, as promised, about melted the headers off my new engine. I tried to work with it later on and eventually chucked the $500 POS in the trash! The carb I have used exclusively was built by Mr. Lloyd Bray whom many old timers may recognize from the early days of the 428CJ Mustang. He is also partner to DG Gulliam with their 428CJ GT/A Mustang. I just had two built and have yet to try them; waiting on getting the car back on the track.
Opposite of Tom's comments on fuel pressure, I have always run 6-6.5PSI without any problems, even driving in the pits. Pushing it to 7#'s causes driving in the pits problems and you have to switch the pump on / off. I'm promised the new carbs will not have that problem and should be able to run more pressure if necessary. But then again, I suspect my fuel system is vastly different than what Tom runs so maybe that's why we're seeing different results.

[Duane Eiskant II]

i dont know about those flow numbers but sounds like the holley 950 which actually is only 830. The 4300D ive run for the last 10 years only flows 580. Now thats real word numbers on the WET flow bench. Im sure it could be more if i dry flowed it but it does have to mix with fuel so thats not actually. No power valve, plug 73 and 86 jetting never change it just leave it alone the flap stuck once last year at kinston at the points race so now i just keep some 3 in 1 oil and check it ALL THE TIME.

[vic guilmino]

did the 4300 come on the 460 fords

[Tom Goldman]

Jeff, the problem with 7# and up of fuel pressure only is an issue when running the oem style secondary needle and seat. ....Not an issue when running only a larger primary needle and seat. .....Tom

[SSDiv6]

Originally Posted by Tom Goldman

Jeff, the problem with 7# and up of fuel pressure only is an issue when running the oem style secondary needle and seat. ....Not an issue when running only a larger primary needle and seat. .....Tom

In the past, I have used the Grose-Jet needle and seat assembly which allows you to run higher fuel pressures without flooding the engine.

They are similar to this picture:



I cannot remember if Jeff Lee tried them ion his carburetor in the past. I have succesfully used them in many foreign car applications, Quadrajets and Webers, allowing me to run higher fuel pressure without overriding the float.