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Motorcraft 4 Barrel Carb

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FSJunkie View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2021 at 3:40am
Is any body else's 4300 particularly persnickety abut it's idle mixture setting?

My emissions sticker says to adjust the idle mixture for a "40 rpm lean drop" and it runs fine if I do that, but if I ignore that sticker and set it to a "best idle" fuel mixture........woah, boy it is not happy!!!! It'll flood rich, bog, and even stall if the fuel is sloshed at low speeds, such as while driving over a speed bump at an angle or turning into a driveway. I mean it will flood and stall in the middle of an intersection and try t get you killed if you set it to a best idle mixture. Follow the 40 rpm lean drop though and it's happy as a clam. 

I know some carburetors that lean or flood on really hard maneuvers like hard stops, but it take a pretty strong lateral g-force to do it. I've never seen one this sensitive. 

I have inspected the float, needles, and settings more times than I can say and this car has always done this, ever since it was new. I know because it's been in my family ever since it was new. 

I'm wondering if it's just me experiencing this...

Maybe there is a reason the police duty 401 used a special hinged float? 
1955 Packard
1966 Marlin
1972 Wagoneer
1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited
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PHAT69AMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/22/2021 at 8:34pm
The 4300 is a wonderful carburetor... no troublesome secondary Venturiis to worry about...
Just strait through secondary passages with boosters and an off-center air flapper valve...
So much better than a Holley with actual secondary Venturiis & Boosters to react to signal, atomize fuel. 

Edited by PHAT69AMX - Oct/22/2021 at 9:54pm
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Metman View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Metman Quote  Post ReplyReply Direct Link To This Post Posted: Oct/25/2021 at 4:52pm
Just to ask.. Is there a rebuild kit for the 4300 that folks like?   Thinking about reinstalling the original 4300 on my 1972 360. 
1972 Javelin/AMX
1960 Nash Metropolitan
1963 Studebaker GT Hawk
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ramblinrev Quote  Post ReplyReply Direct Link To This Post Posted: Oct/25/2021 at 4:56pm
Any fresh kit should be fine.

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70 AMX 360 4-speed (since 1981)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote scott Quote  Post ReplyReply Direct Link To This Post Posted: Oct/25/2021 at 5:28pm
I used a Walker kit # 15410D about 6 months ago. It came with the good blue accelerator pump cup. I bought an extra kit at the same time, so I can say I would use that kit again.

Don't use a black pump cup.
"Prolly" is not a word.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote S Curry Quote  Post ReplyReply Direct Link To This Post Posted: Oct/28/2021 at 8:54am
Maybe I'm deaf dumb stupid and blind. I collected about 3 4300 Autolites for my 70 AMX. After 4 kits at about 40 bucks apiece, Helicoils for the screw in the base that was stripped out....and an engine fire after splitting a fuel line and not catching it after removing the carb after a dozen times or more.....I bought a Holley 600 vacuum secondary return.. was $205 including shipping. Got it in 2 days. Put on, engine started right up and I HAVE not laided a screwdriver on it for the last 5 years..not even idle.....maybe I got lucky....damn it starts and runs good....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic Silver Quote  Post ReplyReply Direct Link To This Post Posted: Oct/28/2021 at 9:57am
Originally posted by S Curry S Curry wrote:

Maybe I'm deaf dumb stupid and blind. I collected about 3 4300 Autolites for my 70 AMX. After 4 kits at about 40 bucks apiece, Helicoils for the screw in the base that was stripped out....and an engine fire after splitting a fuel line and not catching it after removing the carb after a dozen times or more.....I bought a Holley 600 vacuum secondary return.. was $205 including shipping. Got it in 2 days. Put on, engine started right up and I HAVE not laided a screwdriver on it for the last 5 years..not even idle.....maybe I got lucky....damn it starts and runs good....
I bought my 70 AMX new, and abandoned my Autolite 4300 the first time about 35-40 years ago. I finally sent it to the Autolite guru, Pony Carbs, to work their magic. I then put it back on the car for about a month or two, and abandoned it again. It has sat in a box for the last 10-12 years, looking really pretty. Meanwhile the car runs great with a Summit carburetor.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/30/2021 at 10:59pm
Sonic Silver, Summit "4010" holley clones that are silver or the newer Summit "Max Performance" 4150 clones that are black?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic Silver Quote  Post ReplyReply Direct Link To This Post Posted: Oct/31/2021 at 8:58am
Originally posted by PHAT69AMX PHAT69AMX wrote:

Sonic Silver, Summit "4010" holley clones that are silver or the newer Summit "Max Performance" 4150 clones that are black?
The 4010 remakes. I have used both 600 and 750 cfm. I have a 600 on my basically stock SC/360 and a 750 on my modified 360 AMX.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Oct/31/2021 at 9:37am
The problem may be that finding an old core that has not been corroded over time may be a challenge for many. The 4300 aluminum was not at all ethanol resistant and will pit and corrode if this fuel sits in it. Just had one apart the other day were the power valve was sitting looked like a nice O-ring grove was machined into the bore. Pitting everywhere you could see, so likely pitting everywhere you cannot also.
The owner was going to look for a replacement as I didn't think this could reliably be rebuilt.
The 4300 did not look as bad as this:
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