Backfire on Shutdown-'86 CJ7

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  #1  
Old 09-10-02, 02:59 PM
sse01
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Backfire on Shutdown-'86 CJ7

I have an '86 CJ7 with a 4 cylinder that backfires once immediately after turning it off. The backfire is very loud. The backfire occurs only if I have been driving for 10-15 minutes, or more. If I let it idle for 5 minutes before shutting it down, then it does not backfire.

History: I bought it used several years ago. It did not backfire the first year of ownership. If first started backfiring every 3-4 times, and it was not very loud. Now it backfires every time, and it is very loud!

Thanks for your help.
 
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  #2  
Old 09-10-02, 03:12 PM
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likely needs carb work may need rebuilt or replaced it is getting excessive gas into the exhaust causing it to backfire.
 
  #3  
Old 09-13-02, 08:37 AM
sse01
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I have rebuilt this carb twice!!! It is a Carter YFA.

I have found that the main linkage that the butterfly valve is mounted (sorry for the incorrect terminology) has some play in it at the body of the carb. I have tried to have the bushing replaced, but no one has the proper size.

From what I have read, this carb is a dog. I can purchase a rebuilt replacement for $170. My other option is to purchase a better carb made by Weber. Also, I plan to drop a different motor in this vehicle in 3-5. Opinions?

(edited for spelling)
 
  #4  
Old 09-13-02, 09:09 AM
Joe_F
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Carter YFA's are junk. In fact, most Jeeps of this vintage are too

The carburetion and emission controls/quality on these Jeeps were loose and lackluster.

Dropping another engine in it has its own headaches, but can be done. You might run into emission testing headaches with it.

I suggest you have a good shop rebush the base for you and then rebuild it. Make sure you replace all of the expendable parts, such as the choke stat, pull off, gaskets and float. They are old and tired at this point.
 
  #5  
Old 10-14-02, 06:32 AM
sse01
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I have replaced the carb with a Weber. It runs much better, except for it still backfires like described above.

I have looked at the plugs. The front three look normal to me. The rear cylinder's plug looks white, somewhat chalky. I think that this means that this cylinder is too hot. What would cause this?
 
  #6  
Old 10-14-02, 08:57 AM
Joe_F
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How's the condition of the timing chain and the rest of the engine? Could have slack in the chain or a bad valve...
 
  #7  
Old 10-14-02, 10:54 AM
sse01
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A compression test would alert me to a bad valve, wouldn't it?
 
  #8  
Old 10-14-02, 11:37 AM
Joe_F
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Have you done a compression check? What did it reveal?
 
  #9  
Old 10-20-02, 01:34 PM
sse01
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Sorry to take so long to reply.

I did another compression test. All of the cylinders were within 10 psi of each other. The compression seemed to be the same as when I first got the jeep (before the backfire began).
 
  #10  
Old 11-11-02, 12:59 PM
sse01
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I looked at the timing chain and gears. There seemed to be a little slop in them when I put a wrench on the crank and rotated it both directions. I replaced the timing chain and both gears on the crank and the cam. After I installed them, there was much less slop. I still have the backfire.

Here is the following items that have been replaced so far in this search:

Carb
Timing Chain and gears
Points, plugs, & wires


I checked the exhaust system. The catylitic converter is hollow. The muffler was full of the catylist, so I replaced it.


Thanks for any help that you can give me. I feel that at least I am narrowing down the possibilities!!!!
 
  #11  
Old 11-11-02, 06:15 PM
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Join Date: Sep 2002
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I would be looking into the emission controls. Do you have an air pump on that engine? Check out the EGR valve and related circuit/hoses. How is the engine temp...is it any higher than it used to be?
 
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