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Motorcraft 4 Barrel Carb

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LakesideRamblin View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LakesideRamblin Quote  Post ReplyReply Direct Link To This Post Topic: Motorcraft 4 Barrel Carb
    Posted: Jun/09/2019 at 9:34pm
On my 73 Javelin with original (and running 360 engine) I have a Motorcraft 4 barrel carb.  It seems to work well so I'm not messing with it now.  But did AMC use a Ford Motorcraft carbs as standard 4 barrel carbs on their 73 Javelins?  Just curious.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote ramblinrev Quote  Post ReplyReply Direct Link To This Post Posted: Jun/09/2019 at 9:37pm
Yes.
AMC switched to Motorcraft carbs in 1970, and only used their 4-barrels in 360s, 390s, and 401s from then on.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Jun/09/2019 at 10:26pm
I would suggest taking the Motorcraft off for a rebuilding now if it's working and has not had new floats installed. The floats in the carburetor absorb ethanol and "sink" (power valve cup replacement is also ethanol resistant in rebuild kits). The only way to fix this is to replace them, brass after market or the new type:
Just preventative maintenance as more and more fuel is getting ethanol added, like it or not.
My opinion.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jun/09/2019 at 11:03pm
The 4300 is a good carb and flows pretty well.

As far as floats - 
Floats simply go bad - we stocked floats even before ethanol came out so don't be alarmed if you find a carb that needs floats - it's a normal part of life for them - especially 40 years later.
Can't recall how many dozens we'd do because "it's running too rich" and we'd pull them apart and you could squish an area of the float with a thumb nail and gas would come out like a sponge. So they go bad, period. I have personally never had one go bad in a car of mine - but I've replaced a whole lot of them over the years for other folks. Mileage didn't see to matter back then - some just went bad.

When I get the 4300 fully restored (meaning all parts replated and it totally gone through) it's going back on my 70 as it's a better carb than what's on it now. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Buzzman72 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 5:57am
Originally posted by billd billd wrote:

The 4300 is a good carb and flows pretty well.

As far as floats - 
Floats simply go bad - we stocked floats even before ethanol came out so don't be alarmed if you find a carb that needs floats - it's a normal part of life for them - especially 40 years later.
Can't recall how many dozens we'd do because "it's running too rich" and we'd pull them apart and you could squish an area of the float with a thumb nail and gas would come out like a sponge. So they go bad, period. I have personally never had one go bad in a car of mine - but I've replaced a whole lot of them over the years for other folks. Mileage didn't see to matter back then - some just went bad.

When I get the 4300 fully restored (meaning all parts replated and it totally gone through) it's going back on my 70 as it's a better carb than what's on it now. 

 
Amen, Bill.
 
Back in '79-'80 when I first got into AMC parts [for a paycheck], we lined up a source for brass floats for BBD carbs in 258 sixes. Those factory phenolic floats were on borrowed time from the day they left the factory...LONG before ethanol fuels came along.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 7:18am
So Lakeside,
I thought I was giving sound advice on preventative maintenance for your Motorcraft carb. I didn't state anything to replace the carburetor.
The other responses seem to state the floats can be expected to fail, as I did.

I still believe it is sound advice. On these carburetors, it is best to replace the floats, accelerator pump, while the carb is running good. When the floats deteriorate the material will start to plug passages ... and the carb will provide poor performance and cost more to clean and rebuild if allowed to get to that stage.

Take the advice or leave it, just my opinion.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1982AMCConcord Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 8:37am
The 304 engine I bought was out of a 73 Javelin and the previous owner put a cast iron 4 barrel manifold with a rebuilt Motorcraft 4 barrel on it instead. I swapped a Eddy intake on it and it runs really good. Seems like a good carb. I was surprised that it was able to run so well because the carb was for a bigger engine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 8:45am
Originally posted by Trader Trader wrote:

So Lakeside,
I thought I was giving sound advice on preventative maintenance for your Motorcraft carb. I didn't state anything to replace the carburetor.
The other responses seem to state the floats can be expected to fail, as I did.

I still believe it is sound advice. On these carburetors, it is best to replace the floats, accelerator pump, while the carb is running good. When the floats deteriorate the material will start to plug passages ... and the carb will provide poor performance and cost more to clean and rebuild if allowed to get to that stage.

Take the advice or leave it, just my opinion.


Curious - how often did you see floats actually coming apart? They do break down and act like sponges - saw tons of that in the 70s and 80s, but I have yet to see one actually break down as in coming apart!
None of the many dozens I did ever had a float break down in that way. Had one come off the metal lever, however, talk about flooding!!!!!
Just wondering how that looked as I've never seen that over the years. Was it float material or gunk from the tank - because some carbs had a fuel filter that actually went into a bypass mode when plugged.
If a carburetor has not had a kit put in - and yeah some do exist that have never been touched - it's wise to do so in any case. The materials today are superior and it's just plain smart.
I've never switched to brass floats - guess I never had or saw a need, but if you can find 'em, it's a longer life material to be sure and with the push to 15%........ 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LakesideRamblin Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 9:17am
Thanks all for the advice.  I'll get another new set of floats for it.  I may just buy a full rebuild kit just in case I need it.  The engine also has the original cast iron intake manifold.  I will eventually swap that out with a better one (I know there are several good ones from which to choose).  Saw this number on the original manifold behind the carb:  321748B.  Again, I assume it is the original intake manifold.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 9:20am
I have seen about a half dozen of these floats in disintegration, always in cars that have been sitting for several years. Yes they go spongy first but if left to sit they seam to fall apart.
If the owner just tries to get the engine to start then it all goes sideways.
Stale fuel, ethanol, water, hot summers and below freezing winters, don't the exact process but they do disintegrate. Maybe just being by the big lakes and more moisture???
The price point on getting someone to rebuild a carburetor (it has to be completely torn down to clean) compared to replacing it at this stage is pretty much equal so most will replace.
A DYI person can put a rebuild kit and floats in a good running carburetor much cheaper.

Just trying to provide advice from experience. If it's not applicable for all locations, that's fine, ignore it.
I just assumed that others have had/seen the same issues with these carburetors.

   
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