TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > AMC V8 Engine Repair and Modifications
  New Posts New Posts RSS Feed - 4300 motorcraft carbs
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Click for TheAMCForum Rules / Click for PDF version of Forum Rules
Your donations help keep this valuable resource free and growing. Thank you.

4300 motorcraft carbs

 Post Reply Post Reply Page  123 4>
Author
Message
billd View Drop Down
Moderator Group
Moderator Group
Avatar
Forum Administrator

Joined: Jun/27/2007
Location: Iowa
Status: Offline
Points: 23819
Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Topic: 4300 motorcraft carbs
    Posted: May/11/2011 at 11:14pm
I was asked about AMC Motorcraft 4300 carbs, the differences, etc.
I'm going to post what I think I know - feel free to correct me where I'm wrong, and maybe this can be a guide if the info ends up correct....
 
First, the 4300 was used starting in the 1970 model year. In 1970 and 71, AMC used the B/W automatic which had no "kick-down" linkage, it was a vacuum modulator setup. Thus for those 2 years, there will be and should be no linkage for a transmission on either the "automatic" or "stick" version of the carb. If it's got linkage, it's wrong for 70/71, and depending on the linkage, it MAY be a Ford carb, and not an AMC carb. Further, the correct 1970 carb has NO nipple on the back for the PCV - it will have a blind hole, it's not drilled through on the inside.
Many remanufactured carbs used later bodies and the reman company plugged it inside with a plug or epoxy, so just because it's got no PCV nipple and says "for 1970 AMC" does NOT mean it started out life that way. If you've ever been inside a place where they "rebuild" carbs, you'll know why I hate them so much.......
Anyway, here's some examples. I'm not certain exact year that they went to the PCV nipple on the carb, but know for at least 1970, this was in the spacer and not the carb body itself.
 
First - a true 1970 carb from an AMC showing lack of ANY kickdown linkage, and no PCV nipple.
They will have a dashpot, and a nipple for the fuel inlet, not a filter.
 
 
Next is another, same thing - proper 1970 AMC 4300. The nipple at the back just under the air cleaner ledge/air horn is for the fresh/clean air intake tube going to the choke heater.
 
 
This is what I believe to be a 1972 AMC carb - with the kickdown linkage low on the throttle and with the PCV nipple:
 
 
Finally, a couple of FORD 4300s. One I KNOW is off a Lincoln... note the kickdown linkage high on the throttle - the Ford carb pushed the linkage back when the throttle opened, the AMC carb PULLS the linkage forward as you open the throttle.
 
 
 
 
Back to Top
71SC360 View Drop Down
AMC Addicted
AMC Addicted
Avatar
Charter Member

Joined: Jun/29/2007
Location: Western, NY
Status: Offline
Points: 3359
Post Options Post Options   Thanks (0) Thanks(0)   Quote 71SC360 Quote  Post ReplyReply Direct Link To This Post Posted: May/11/2011 at 11:23pm
70 & 71 are the same
Back to Top
ramblinrev View Drop Down
Moderator Group
Moderator Group
Avatar

Joined: Dec/28/2008
Location: Wisconsin
Status: Offline
Points: 4073
Post Options Post Options   Thanks (0) Thanks(0)   Quote ramblinrev Quote  Post ReplyReply Direct Link To This Post Posted: May/11/2011 at 11:26pm
Bill:
I think you're on the right track. Your pic of a '72 AMC 4300 would be for an automatic. The 4-speed version will-I think-look like the '70-71 carbs with no kick down linkage. BTW, kickdown on our '70-71 Borg Warners was accomplished with the electrical switch attached to the accelerator assembly under the dash. The modulator serves other funtions! (I know you know that!)
 
I have several correct '70's, a Ford version for parts, and a '72 or 73 AMC 4300 in my parts closet. I'll pull that one out and see what the linkage looks like.
74 Hornet Hatchback X twins
62 American Convertible
70 AMX 360 4-speed
70 Javelin SST 390
Back to Top
purple72Gremlin View Drop Down
AMC Addicted
AMC Addicted
Avatar
Charter Member

Joined: Jul/01/2007
Location: Illinois
Status: Offline
Points: 11870
Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: May/11/2011 at 11:39pm
Just to add,  I believe all 4BBLs from 1970-78 was motorcraft. think in 1975, started using the 4350, which has it own weird pattern on the manifold. and the 4350 had its set of problems too.
Back to Top
billd View Drop Down
Moderator Group
Moderator Group
Avatar
Forum Administrator

Joined: Jun/27/2007
Location: Iowa
Status: Offline
Points: 23819
Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/11/2011 at 11:48pm
Originally posted by ramblinrev ramblinrev wrote:

Bill:
BTW, kickdown on our '70-71 Borg Warners was accomplished with the electrical switch attached to the accelerator assembly under the dash. The modulator serves other funtions! (I know you know that!)
 
 
 
Yes, but one some transmissions - the MOPAR as used by AMC, for example, they call it "kickdown" but it's really serving the same purpose as the modulator - press the throttle and the linkage moves a spool valve to control "throttle pressures" in the transmission. So in a sense, it's working the same job as the modulator - and the kickdown switch.
Ford is different of course.  But for AMC, the kickdown linkage use more closely functions as the modulator - until or unless you floor it.
MOPAR linkage controls throttle pressure.
B/W modulator controls throttle pressure.
I guess that's where I drew the comparison.
 
Yes, my 72 AMC carb IS for an AMC automatic with the mopar transmission.
The 1972 4300 would look just like  the 1970/71 as far as the throttle linkage.
Back to Top
SuperStockAMX View Drop Down
AMC Apprentice
AMC Apprentice


Joined: Dec/29/2009
Location: Anthem, Arizona
Status: Offline
Points: 237
Post Options Post Options   Thanks (0) Thanks(0)   Quote SuperStockAMX Quote  Post ReplyReply Direct Link To This Post Posted: May/13/2011 at 12:28am
I went 10.50's with one in Stock Eliminator and 10.00's in Super Stock Eliminator. It is an excellent carb that really doesn't require much to be race worthy. I had my friend Bob Green buy one restored from Pony Carbs in NM for his restored '70 AMX and not only did it look great, it ran perfect (390 4-speed) right out of the box. No transition problems from idle to WOT. 
FYI - I've spent plenty of time on the dyno trying bigger and smaller air bleeds and factory engineered is spot on. Jets (there are only two) should be drilled as stock can be lean. Opening up from stock (about .062") to around .068" will probably make a big difference for 90% of you. I seldom go bigger than .072". 
Also, the rear secondary linkage, if you disconnect it and flip it over the secondary will open all the way. Stock it opens about 85%. It won't make that much of a difference but it wont hurt anything. 
And use the TOMCO rebuild kit. It is much better. 
Back to Top
SKeown View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jul/30/2009
Location: Texas
Status: Offline
Points: 2396
Post Options Post Options   Thanks (0) Thanks(0)   Quote SKeown Quote  Post ReplyReply Direct Link To This Post Posted: May/13/2011 at 1:00am
Originally posted by SuperStockAMX SuperStockAMX wrote:

I went 10.50's with one in Stock Eliminator and 10.00's in Super Stock Eliminator. It is an excellent carb that really doesn't require much to be race worthy. I had my friend Bob Green buy one restored from Pony Carbs in NM for his restored '70 AMX and not only did it look great, it ran perfect (390 4-speed) right out of the box. No transition problems from idle to WOT. 
FYI - I've spent plenty of time on the dyno trying bigger and smaller air bleeds and factory engineered is spot on. Jets (there are only two) should be drilled as stock can be lean. Opening up from stock (about .062") to around .068" will probably make a big difference for 90% of you. I seldom go bigger than .072". 
Also, the rear secondary linkage, if you disconnect it and flip it over the secondary will open all the way. Stock it opens about 85%. It won't make that much of a difference but it wont hurt anything. 
And use the TOMCO rebuild kit. It is much better. 
 
 Naturally if you're hoping to run like Jeff's car, be prepared to spend money to have it tricked to flow a couple hundred more CFM. That's if you want the whole story...lol
 
 SKeown
Back to Top
SuperStockAMX View Drop Down
AMC Apprentice
AMC Apprentice


Joined: Dec/29/2009
Location: Anthem, Arizona
Status: Offline
Points: 237
Post Options Post Options   Thanks (1) Thanks(1)   Quote SuperStockAMX Quote  Post ReplyReply Direct Link To This Post Posted: May/13/2011 at 2:01am
Well...since you probably don't have a rule book, I'll tell you that in both classes you are not allowed to port or polish, thin the blades or anything else that will yield more CFM. Can't even take the choke off. And NHRA does check for this kind of thing. Often. And I, as others in the class, have been checked more than once by the best. 
Anybody wants to take a look at it alongside their own Autolite is more than welcome! 
Back to Top
SKeown View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jul/30/2009
Location: Texas
Status: Offline
Points: 2396
Post Options Post Options   Thanks (0) Thanks(0)   Quote SKeown Quote  Post ReplyReply Direct Link To This Post Posted: May/13/2011 at 2:12am
Originally posted by SuperStockAMX SuperStockAMX wrote:

Well...since you probably don't have a rule book, I'll tell you that in both classes you are not allowed to port or polish, thin the blades or anything else that will yield more CFM. Can't even take the choke off. And NHRA does check for this kind of thing. Often. And I, as others in the class, have been checked more than once by the best. 
Anybody wants to take a look at it alongside their own Autolite is more than welcome! 
 
 Sure Jeff, and you're heads and intake fit the guidlines too. Besides that you didn't dupe NHRA into allowing replacement pistons with gobs more compression. Who do you think you're kidding? I'm not saying you're the worst cheat out there, I am saying you're among the worst and a hypocrite to boot!
 
 SKeown
Back to Top
Hurst390 View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Apr/20/2008
Location: Decatur Ill
Status: Offline
Points: 2550
Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst390 Quote  Post ReplyReply Direct Link To This Post Posted: May/13/2011 at 7:02am
tomco...you acutally use a tomco needle and seat? They have to be the worst needle and seats I have ever used...the rest of the kits are fine but tomco needle and seats belong in the trash..unless they have changed recently
SC/Hurst Rambler

11.62 120

100% Street Legal
Back to Top
 Post Reply Post Reply Page  123 4>
  Share Topic   

Forum Jump Forum Permissions View Drop Down



This page was generated in 0.188 seconds.
All content of this site Copyright © 2012 TheAMCForum unless otherwise noted, all rights reserved.
PROBLEMS LOGGING IN or REGISTERING:
If you have problems logging in or registering, then please contact a Moderator or