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Concord Engine Shakes Violently When Turned Off

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jrbuzz View Drop Down
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    Posted: Oct/22/2017 at 8:46pm
So, we’ve gotten the 1982 Concord up and running and it’s been doing great. The carb was rebuilt and most of the exhaust (from the manifold to the muffler) was replaced. It has the 4 cylinder Iron Duke engine (I had no idea where to post this thread!) and my sister, who drives the car, has been complaining of the engine shaking when it is turned off. It previously was not an issue and was very minor, at worst. But now she says it is so violent that the entire car moves when it is shut off. What could be causing this issue suddenly?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Midnight Rambler Quote  Post ReplyReply Direct Link To This Post Posted: Oct/23/2017 at 7:52am
Dieseling.  Check the timing.  It's probably not carbon build up if it came on strong all of a sudden.  You say the carb was rebuilt so it doesn't need to be cleaned but it may be leaking fuel into the intake or something.  It's usually carb, timing, or carbon.  The carb was worked on, so that's the easy guess.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote carnuck Quote  Post ReplyReply Direct Link To This Post Posted: Oct/23/2017 at 9:06am
Vacuum leak or too high of an idle affects it too. Wrong PCV valve caused this on the carbed 2.5 AMC 4 cyl in an ‘84 Cherokee. It was hard to start after a tuneup was done and RPMs popped up a couple hundred at idle but couldn’t be adjusted down.
   My Comanche had a similar tuneup before I got it. They added a “missing” PCV in the CCV system and wondered why it ran so poorly.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jrbuzz Quote  Post ReplyReply Direct Link To This Post Posted: Oct/23/2017 at 10:40pm
Alright what can I do to check the timing? I’ll be honest, I’m new to some of the more advanced things like that with this car. Also, In regard to the PCV, what am I looking for? Where am I looking? Adjusting this carb is near impossible because of the way it’s positioned. You can’t get to the adjustment screws because they’re up against the firewall.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Oct/24/2017 at 7:18am
Well, the easy way is to just loosen the distributor and turn it a slight amount, see if that helps. Note where it is before you move it, then loosen and twist it about 1/4" (NOT 1/4 turn!!) in either direction, tighten, then drive. If it gets worse or doesn't help, try the other direction. If that doesn't help return to where it was -- it's not timing. When I say "move about 1/4" " I mean look at something like the vacuum advance. Move it about 1/4" from where it is....

Look at the motor mounts. Fours always shake more, and the mounts are made to absorb some of that. So the mounts get a lot more wear than on other engines. If one has come apart even partially that could be the issue. Try to rock the motor by hand while looking at the mounts. The driver's side mount usually goes first.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote carnuck Quote  Post ReplyReply Direct Link To This Post Posted: Oct/24/2017 at 8:46am
The distributor is made so the vacuum advance “pulls” the timing forward. IIRC, ccw is advance. Too much gets ignition kickback. The idle gets set last. Check for loose intake bolts and that your carb’s through bolts aren’t loose. My apologies on the PCZv thing. It was more to point out previous owners do all sorts of weird stuff when they don’t have a clue.

Edited by carnuck - Oct/24/2017 at 8:50am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote one bad rambler Quote  Post ReplyReply Direct Link To This Post Posted: Oct/24/2017 at 8:48pm
Some carbs have an anti dieseling solenoid....make sure it`s working correctly...also try higher octane fuel
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amcenthusiast Quote  Post ReplyReply Direct Link To This Post Posted: Oct/24/2017 at 8:57pm
Get your Chilton's 75-'82 AMC Repair Manual to go along with the car -Chilton's has an excellent troubleshooting section that should help you narrow it down to the root cause of the problem.

(since I am not 'The Amazing Kreskin") Without seeing your engine compartment first hand, but since that'll have an electronically controlled carburetor I'd make quick visual scan for loose vacuum lines unplugged wire connectors etc ...my first thought is that it has a malfunctioning electronically controlled throttle solenoid or maladjusted throttle stop device setting causing run on, when hot, & shut down... maybe just needs 'babysitting' and a little more fine tuning .. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jrbuzz Quote  Post ReplyReply Direct Link To This Post Posted: Oct/25/2017 at 8:07pm
Alright, excellent. I will most definitely be posting more on here in regards to questions when I get to take a look at it. I will check the things mentioned here with my Chilton’s manual (very, very useful!) and see how it goes.
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