motorcraft 4300 carb info
 

any one running a motorcraft 4300 carb,looking for some on set up any info would be helpful,tom thanks for you info thanks gmonde

Re: motorcraft 4300 carb info
 

i run the 4300D on my combo love it. back to back with dads 780 holley off his 71 runs the same..

Re: motorcraft 4300 carb info
 

what CFM is the motorcraft Duane?

Re: motorcraft 4300 carb info
 

on the wet flow bench at work its a hole 580

Re: motorcraft 4300 carb info
 

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.

Re: motorcraft 4300 carb info
 

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

Re: motorcraft 4300 carb info
 

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

Re: motorcraft 4300 carb info
 

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

Re: motorcraft 4300 carb info
 

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.

Re: motorcraft 4300 carb info
 

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

Re: motorcraft 4300 carb info
 

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! ;)

Re: motorcraft 4300 carb info
 

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)!

Re: motorcraft 4300 carb info
 

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

Re: motorcraft 4300 carb info
 

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

Re: motorcraft 4300 carb info
 

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

Re: motorcraft 4300 carb info
 

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.

Re: motorcraft 4300 carb info
 

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.

Re: motorcraft 4300 carb info
 

did the 4300 come on the 460 fords

Re: motorcraft 4300 carb info
 

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

Re: motorcraft 4300 carb info
 

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:

http://www.minimania.com/imagesbig/aud9096gr.jpg

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.

Re: motorcraft 4300 carb info
 

Vic, yes the 4300D came on many 460`s, but it seems that all the 460`s in the SS/GT classes run the 74 version, which had a Carter ThermoQuad available as well as the 4300D.

Re: motorcraft 4300 carb info
 

i use both needle and seat assemblies in the carb. Primary and aux, and run 9 # of fuel pressure. No flooding issues. Also since the float bowl area is so small i run a number 10 line from the regulator to the carb inlet which helps act as a log and hold reserve fuel.

Re: motorcraft 4300 carb info
 

Duane, whose needle and seat do you use? ... I'd love to be able to run both ,but always had problems with the aux flooding. ....I also use the big line to the carb...... BG reg and pump.........Probably i'm being cautious too, since the AMC factory rebuild kits did away with the aux inlet back in the late ' 70's.....Planning to take the car to the Dutch Classic, I'll have to try running the aux, if the air is good it'll need all the fuel it can get.. ..... .Tom

Re: motorcraft 4300 carb info
 

I've always run both the primary and secondary needle and seat assemblies. I do run a return style regulator. Like I said, just under
7#'s has not been an issue.
I did purchase one ofthe Gross-Jet assemblies. They sent the wrong p/n twice and I gave up. Never did get my money back either!

Re: motorcraft 4300 carb info
 

who sell the grose assemblys???? ,like tom mentioned the rebuild kits that you get today dont have the aux needled and seat they come with a plug

Re: motorcraft 4300 carb info
 

gmonde--I sent you a PM--Comp 387

Re: motorcraft 4300 carb info
 

D & G Valve Manufacturing CO Inc
8 Mount Vernon Street
Stoneham, MA 02180
(781) 438-1789

...also, contact Larry Fulton at Hot Rod carbs...

http://www.hotrodcarbs.com/precisionFlow.html

Re: motorcraft 4300 carb info
 

Tom, i made my needle and seat. Use the same needle and drilled the seat bigger i think i got it like .120 or so cant really remember. Havent had any problems with it so ive left it alone. The aux needle and seat assembly was in the carb and ive never changed it.

Re: motorcraft 4300 carb info
 

Same thing here...

Re: motorcraft 4300 carb info
 

Same thing I did on mine, drilled to .120". .......I'll have to see if I can scrounge up an aux needle and seat to try. I typically run 7#, 9# in good air with just the one inlet, but I know when I jet it up in really good air,it tends to nose over at about 1200'.. .....You can see the A/FR go lean at that point,so the aux valve will definately help .....Suprisingly this is the most anyone has been willing to talk about these carbs. .....The few Ford guys who run them are usually very protective of their info. ........Tom

Re: motorcraft 4300 carb info
 

i drilled mine as well but didnt go as big in fear that the bigger hole would push the needle back easier under more presure ,flooding the engine gmonde

Re: motorcraft 4300 carb info
 

Tom send me a email i think i have few extra aux needle and seat assemblies ill send you one.
Duane Dee9275@yahoo.com

Re: motorcraft 4300 carb info
 

Thanks Duane. ....You have a PM. ....Tom