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1978 AMX Sputters and Stalls

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matador64 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matador64 Quote  Post ReplyReply Direct Link To This Post Topic: 1978 AMX Sputters and Stalls
    Posted: Jun/16/2019 at 7:17am
My wife has a 78 AMX, beautiful car and I'm certainly not a mechanic but know some stuff.
258 inline 6 - 2 barrel carb.
Plenty of gas in the tank, take really clean. It'll run awesome for quite some time and many miles, but then this happens frequently. The car will just bog down, sputter, backfire, almost feeling like it runs out of gas with no power and then it will just stop and engine stalls.
It'll start right up but then will do it again after several more miles.
Boy it makes her upset rightfully so. 
Anyone had this problem before and suggestions??
Thanks for help

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304-dude View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Jun/16/2019 at 7:49am
Could be due for a carb rebuild. Modern gas and years of use can allow for crud build up and leaks.

Most likely a leaky power valve... but long ago a friend had an issue very much like what you have explained. It turned out to be the coil. Mostly csn be replicated once at operational temp. Only ran well when engine was cold or not completely warmed up.

Some will look for model 2100 series from a 304 as a better option. Though it may require an adapter / spacer, not sure, but that's what ended up with my 2100, and there are some threads on going that route.

It all depends on how much you want to put into it.



Edited by 304-dude - Jun/16/2019 at 7:58am
71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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purple72Gremlin View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Jun/16/2019 at 8:23am
when it acts up....makes me think fuel pump.  But if it is a sudden type thing. May be ignition. How lomg since it been tuned up?  
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matador64 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matador64 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/16/2019 at 8:27am
Thanks for all's quick response as us AMC folks are certainly a specific type of car collector. I've had 8 AMC's but now have an 86 442. Sorry I couldn't resist.
I'm leaning toward fuel pump too and I know I can do that myself and isn't expensive.
The car was restored and engine rebuilt some 25 years ago but then sat for a lot of year. Engine is pin clean.
Heck, I know it could be several problems, that's THE PROBLEM.
What I do know when it sputters out of the blue when running down the road, it'll backfire a little then you can certainly smell gas!!!!!
Thanks Cory


Edited by matador64 - Jun/16/2019 at 9:55am
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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 Posted: Jun/16/2019 at 10:22am
Just replaced my fuel pump on my 69 Rambler.  Engine has only around 1,000 miles on it (360).  The diaphragm inside was toast due to the new type gas.  Replaced and it is fine.  I will buy another as a spare and keep it in the trunk.  
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"If you could kick the person in the pants responsible for most of your trouble, you wouldn't sit for a month." T. Roosevelt
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Trader View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Jun/16/2019 at 11:15am
Another possibility is the fuel holes. My tractor did exactly as you state and I took the carburetor apart to find little pieces of gooey rubber in it.
Cleaned the carburetor and replaced the fuel hose (put a screwdriver down the hose and it pulled out all black, gooey) with ethanol resistant and all has been well.
As others have stated, a carburetor rebuild but all the rest of the rubber bits in the system as well would be a good idea.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 73Gremlin401 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/16/2019 at 2:35pm
Originally posted by matador64 matador64 wrote:

My wife has a 78 AMX, beautiful car and I'm certainly not a mechanic but know some stuff.
258 inline 6 - 2 barrel carb.
Plenty of gas in the tank, take really clean. It'll run awesome for quite some time and many miles, but then this happens frequently. The car will just bog down, sputter, backfire, almost feeling like it runs out of gas with no power and then it will just stop and engine stalls.
It'll start right up but then will do it again after several more miles.
Boy it makes her upset rightfully so. 
Anyone had this problem before and suggestions??
Thanks for help



if this car is a very early-build 78, and the ignition system is original to the car, it may have the Prestolite ignition module and distributor.  The symptoms you are describing are classic for how these act when the module is tired, or when the vacuum advance diaphragm is ruptured at the distributor.  If it is a later 78-up Motorcraft ignition, then swapping out the module next to the battery with a good quality (Standard Ignition or Motorcraft) module should make this go away.  If it is Prestolite, first thing to do is confirm the vacuum advance is OK - disconnect the hose from the vacuum source and suck on it.  If there is no resistance, then the diaphragm is bad in the distributor, and the sputtering/backfire is caused by gas fumes getting in the distributor, and exploding. Rebuild kits or reman distributors are still available and cheap.  if vacuum resistance is there, then swap out the module and that should sort it out.
73 Gremlin 401/5-spd.
77 Matador Wagon 360/727.
81 Jeep J10 LWB 360/4-spd
83 Concord DL 4-dr 258/auto

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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: Jun/16/2019 at 3:01pm
? 1978 Ford DuraSpark Electronic Distributor Pick-Up in Distributor or Brain Box ?
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firefly View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote firefly Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2019 at 9:55am
I'd get rid of the presto lite and go HEI and be done with it. If you smell gas, it's not the fuel pump.
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