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post #1 of (permalink) Old 12-19-1999, 03:30 PM
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HELP! Backfire through Carb

I was in a hard acceleration and next thing I know I have a loud backfire though the carb. The motor is a 304. I just got the jeep not too long ago. I have not check the timing on it yet. Could the dist. slip or the chain jump? Any help would be great. Thanks, Carl

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post #2 of (permalink) Old 12-19-1999, 03:36 PM
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Re: HELP! Backfire through Carb

Could be several things but not really enough info.
It's not the dist. slipping(jumped a tooth) or timing chain if it is still running normal. Either one & it runs really bad[img]/wwwthreads_images/icons/frown.gif[/img] or does'nt at all[img]/wwwthreads_images/icons/mad.gif[/img]

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post #3 of (permalink) Old 12-19-1999, 03:40 PM
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Re: HELP! Backfire through Carb

It runs but I had to take the #4 plug wire off, in order to limp home. What other info do you need?

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post #4 of (permalink) Old 12-19-1999, 04:31 PM
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Re: HELP! Backfire through Carb

Take a timing light to it ......set the timing.......if you can't align the marks ..........plan on changing the timing chain........ If you have a "dial advance" feature on it and need some really strange "offset" to get "virtual" TDC ...... it kinda indicates the chain is jumping. If you can adjust the timing within limits ..........check it in a few days.....if the timing has changed ......this usually also indicates that the chain needs replacement.

Have you checked the cap?

If for some reason the distributor has "jumped" (I've never had this happen to me) ..........it should not prevent you from adjusting the timing.....the distributor, WITH THE EXCEPTION OF PHYSICAL OBSTRUCTIONS, could care less which tooth is where nor which direction/side the vac advance is facing .........as long as when # 1 piston is at TDC ......the rotor is pointing at #1 plug wire on the cap.

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post #5 of (permalink) Old 12-19-1999, 05:13 PM
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Re: HELP! Backfire through Carb

Why did you have to take off #4 plug wire? Did it keep backfiring with it on? There is a chance it could
be crossfire between plug wires but I'm never that lucky, hope you are. Otherwise, my guess is #4
intake valve is not closing. Hopefully, it's just burnt and didn't go through the top of the piston. Do a
compression test. Check the oil, does it smell like gas?




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post #6 of (permalink) Old 12-19-1999, 05:38 PM
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Re: HELP! Backfire through Carb

I took the #4 wire off so it wouldn't throw fire though the carb. I could still hear a small backfire under load. when the Jeep wasn't under load, the Jeep sounded fine. I will check the timing and the oil when I get home tomorrow. I had the valve cover off but couldn't see anything. I hope it is not a valve. Thanks, Carl

post #7 of (permalink) Old 12-19-1999, 06:52 PM
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Re: HELP! Backfire through Carb

I had a similar problem a while ago. At first I thought it was a burnt valve/malfunctioning valve, but after I replaced the plug wires I got REAL lucky and it was the wires..even thoug they were only 1 month old....there was a small defect in the insulation boot. try switching two of the same length plug wires around......or look under your hood at night when its real dark and look for spark.

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post #8 of (permalink) Old 12-19-1999, 09:54 PM
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Re: HELP! Backfire through Carb

Check the inside of the dist. cap where all the plug wire leads come through. You may have some carbon arcing (it will look like a pencil line) going from somewhere to #4. This is odd that it would be so consistent though. Carbon tracking is usually intermittent because it is never a really good conductor (unless it is REALLY bad).

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