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post #1 of (permalink) Old 05-26-2005, 11:22 AM
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new Carb options for J-20 with an AMC 401 ??

I have a 1976 jeep J-20 pickup with an AMC 401 engine, and am having some problems with it. I've come to the conclusion that it may have something to do with the Carb and want to replace it.

My question is if there are any aftermarket carbs that will mate with the stock AMC manifold with little or no serious modifications??
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post #2 of (permalink) Old 05-26-2005, 11:36 AM
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Re: new Carb options for J-20 with an AMC 401 ??

don't bother unless you're going fuel injection. the MC2100 is the best Carb for the AMC V8's. If you think the problem is the carb, you may consider getting a rebuild kit for it and rebuiliing the carb. they are so damn simple.

What kind of issues are you having. it may not be the carb. let us know and maybe we can help you save some time and money.
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post #3 of (permalink) Old 05-26-2005, 11:55 AM
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Re: new Carb options for J-20 with an AMC 401 ??

This is actually my dads truck, but me and him basically share it and he hasn't the time to do a lot of work on it, so its up to me I guess.
The symptoms I'm seeing are as follows:

Starting the engine can be a bit hard, as it will sometimes stall out. to keep engine going I need to hold the throttle down for a while until it warms up a bit.

Once warmed up, it seems to run ok for a bit, but after the engine is at or above normal operating temps, it will sputter and die at low RPM when under load. Seems to idle properly in neutral, but if you try to put it in gear it will sputter and die. To start off from a red light I have to rev the engine a little and drop into gear to keep from stalling. While driving, if I try to accelerate quickly up a hill, or even on flat ground, the engine will stutter and loose power until I reduce throttle. When reversing the truck, the problem is magnified substantially. I have to hold the RPM quite high while reversing to keep from stalling out.

I've tried some troubleshooting, although I'm not a mechanic myself. I've taken it to the shop to have the timing and carb adjusted, and this seemed help a little (and I mean barely noticeable).
I was planning on replacing the carburetor as it is in piss poor shape. I've also read a lot and it's been suggested that a fuel pump could cause similar problems, but this doesn't explain why the problem gets worse as the engine gets hotter. I've also replaced components in the EGR system but they just keep failing. Which is one of the reasons I wanted to scrap it and go to a new carb with an electric choke.
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post #4 of (permalink) Old 05-26-2005, 12:29 PM
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Re: new Carb options for J-20 with an AMC 401 ??

In stock form, the AMC 401 used in Jeeps came with a four barrel cast iron intake and Motorcraft 4 bbl carb. If you can get it rebuilt properly by a good mechanic, it should give you many years of good service. Going down to a 2 bbl Motorcraft wouldn't be a choice I'd consider, if you have the 4 bbl intake. Other new 4 bbl options are Edelbrock Q-jet, (now discontinued), Edelbrock Performer or Holley, (my least-favorite carb). I believe the 4 bbl Motorcraft is a spread-bore carb. If so, then an adapter would be needed to switch to a square-bore like the Edelbrock Performer or Holley. Fuel pumps are relatively inexpensive, you might want to try replacing it first to see if that helps.
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post #5 of (permalink) Old 05-26-2005, 12:43 PM
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Re: new Carb options for J-20 with an AMC 401 ??

have you swapped fuel filters yet? another cheap item that can give some of those symptoms. Also you need to check for Vaccum leaks. around base of carb is pretty typical if the carb has been removed or disturbed. Also all your vaccum hoses should be checked. a quick test for vaccum leaks is to get theengine to idle. remove air cleaner, and cover the carb intake with your hands. if it doesn't die down and stall pretty quick, you have a vacuum leak and it's pulling air from somwhere it shouldn't be. that would mean you're running lean (too much air flow) also check that your choke is working properly. that it's choking when cold and opening up when warmed up.
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post #6 of (permalink) Old 05-26-2005, 12:55 PM
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Re: new Carb options for J-20 with an AMC 401 ??

Yeah I definatley wouldn't want to go down to a 2 barrel Carb. I know the carb we have has been rebuilt at least once since we've had it, and we don't put alot of miles on it as it isn't a daily driver. just used for hauling and to go off road during hunting season.

One other thing, we suspect that there may be something wrong with the manifold on ours. Possibley slightly warped, at least where the caruretor mounts. Ever time we have taken off the carburetor to be worked on and re-installed it, the spacer/gasket soon cracks on the same corner every time. Could this also be a cause? and is there anyway to fix this without replacing the manifold?
post #7 of (permalink) Old 05-26-2005, 01:01 PM
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Re: new Carb options for J-20 with an AMC 401 ??

The choke on this one is always giving us problems (yet another reason Dad wants to replace it with one that has electric choke)and we're just gettin tired of dealing with this finicky P.O.S.

PS.The fuel filter is also new
post #8 of (permalink) Old 05-26-2005, 02:46 PM
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Re: new Carb options for J-20 with an AMC 401 ??

[ QUOTE ]
the spacer/gasket soon cracks on the same corner every time.

[/ QUOTE ]

This could well be the root of many of your problems. It's a sign that either the manifold or the carburetor is seriously warped. The manifold would need to be removed and placed on a milling machine to flatten it out.

At any rate, it sounds like you have vacuum leaks somewhere. Best way to find them is by spraying carb cleaner around every place that has vacuum - manifold, carb base, all hoses, diaphragms and so on - while the engine is idling as slowly as possible. Take your time, because what you're looking for is a change in idle speed as the spray is sucked into a leak.
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