Backfiring- timing or carb? - JeepForum.com

 
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post #1 of 12 Old 06-12-2013, 09:44 PM Thread Starter
WNC-84CJ7
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Backfiring- timing or carb?

My J20 backfires a lot. It does it when I downshift and the lower gear causes a slow down- it does it sometimes in the lull during the upshift. Dad says to advance the timing. I was also wondering if it could be a carb adjustment? I am about to swap out the leaky headers- I am probably going to go back to manifolds if I can find a reasonable set. Good headers would be cool, but I only want to do this once.

I have quite a few questions. Would the timing advance help? Do my leaky headers have anything to do with it? Can I do the timing myself? If so, do I need any special tools, like a light or something?

AMC 360, with long headers to Magnaflows, and the carb below.

I have SO many other questions, but I'll stop there- sort of. I don't want to get flamed or sound like an idiot, but how can I tell if my carb is two or four barrel?





It does say Motorcraft. Many more dumb questions to follow, as I now have two 30+ year old Jeeps.


"No free man shall ever be debarred the use of arms. The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government"
-- Thomas Jefferson, 1 Thomas Jefferson Papers, 334

Last edited by WNC-84CJ7; 06-12-2013 at 09:46 PM. Reason: add
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post #2 of 12 Old 06-12-2013, 10:03 PM
lucdog
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I thought we determined the carb was a 4bbl. Open up the butterfly's on the back and look down inside.
A timing light is needed to set timing.
Backfiring on deceleration can be caused by exhaust leaks.
I would go with factory manifolds.

1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1979 J20
1980 CJ5 trail Jeep.
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post #3 of 12 Old 06-12-2013, 10:07 PM
lucdog
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This screen shot shows what I believe to be the linkage to open the rear butterfly's .

image-2757500083.jpg

1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1979 J20
1980 CJ5 trail Jeep.
1983 CJ7
1989 YJ the CJ to YJ.
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post #4 of 12 Old 06-12-2013, 11:40 PM
LumpyGrits
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Set your timing to OEM specs and go from there.
Take your fuel filter and put the return line(smaller dia.)at the top.
Do you have a vac. gauge?
YES, you need a timing light to set the timing......
LG
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post #5 of 12 Old 06-13-2013, 04:59 AM
Matt1981CJ7
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Quote:
Originally Posted by WNC-84CJ7 View Post
My J20 backfires a lot.

Do my leaky headers have anything to do with it?
Yes, your "leaky headers" are probably the sole cause of your backfiring.

Fix that, before you do anything else.

Matt
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post #6 of 12 Old 06-13-2013, 05:45 AM
pman
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I'm pretty sure that's an old 4350 (4 barrel). X2 to Matt, Bill and LG's suggestions!

88 Wrangler Laredo 258-999-NP231
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post #7 of 12 Old 06-13-2013, 06:27 AM Thread Starter
WNC-84CJ7
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Thanks fellas. Yes- I will start with the return to manifolds. Bill, I know we looked at and discussed the carb a little bit, but we never really named its type, and I am so not "automotively inclined" that I didn't know if it was 2 or 4. That snapping has got to go! Thanks again guys.

"No free man shall ever be debarred the use of arms. The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government"
-- Thomas Jefferson, 1 Thomas Jefferson Papers, 334
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post #8 of 12 Old 07-10-2013, 03:32 PM Thread Starter
WNC-84CJ7
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OK, exhaust leak is history. It's amazing what a few header bolts will do. I am still intending on going back to headers. However, seeing as it runs MUCH better, and I am so close on the CJ, I will wait a bit for those. The CJ needs to eat some dollar$.

It still backfires a good bit. Almost always on the upshift, and when I downshift, and the tranny slows me down. I want to start with the most likely candidate, and work my way back. So the original question remains- timing or carb?

If it is timing, I guess I need a light, and a freakin' clue how to do it. If it's the carb... I guess it will just backfire- carbs terrify this guy. Where do I start?

Chris

"No free man shall ever be debarred the use of arms. The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government"
-- Thomas Jefferson, 1 Thomas Jefferson Papers, 334
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post #9 of 12 Old 07-10-2013, 04:16 PM
LumpyGrits
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You start with a copy of the Factory Service Manual.
And GOOGLE......
Basics of ign timing.
LG
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post #10 of 12 Old 07-10-2013, 04:43 PM
86cj74.2L
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When was the last time you did a tuneup?

Have you ever set the idle mixture screws?
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post #11 of 12 Old 07-10-2013, 04:54 PM
hmantractors
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Tuneup

Hope your harmonic balancer has not slipped. If so will have to time it by ear. The timing lite will give a false reading. I would set #1 to top dead center and make sure the timing marks are correct on the balancer.
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post #12 of 12 Old 03-13-2014, 09:10 PM
70worm
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Looks like a 4bbl ford carb
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