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Unread 06-12-2013, 09:44 PM   #1
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.

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Last edited by WNC-84CJ7; 06-12-2013 at 09:46 PM.. Reason: add
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Unread 06-12-2013, 10:03 PM   #2
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.
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Unread 06-12-2013, 10:07 PM   #3
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
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1957 WILLYS pickup, needs work.
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac trail Jeep.
1979 J20
1980 CJ5 trail Jeep.
1983 CJ7 pretty weekend and sometimes to work Driver in the summer, My first rebuild, if the Q-trac and 5 are broke, this one is the one to take. its just as capable as the other 2, except nice paint.
1984 Grand Wagoneer, 1 ton axles, great 360/727, and a big a$& tree fell on it .
1989 YJ the CJ to YJ conversion.
2005 TJ Rubicon.
2011 Grand Cherokee Laredo 4x4, Mrs. LUCDOG's DD.
Lots of parts not for sale, i'm a hoarder.
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Unread 06-12-2013, 11:40 PM   #4
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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Unread 06-13-2013, 04:59 AM   #5
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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Unread 06-13-2013, 05:45 AM   #6
pman
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I'm pretty sure that's an old 4350 (4 barrel). X2 to Matt, Bill and LG's suggestions!
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Unread 06-13-2013, 06:27 AM   #7
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.
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Unread 07-10-2013, 03:32 PM   #8
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
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"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"
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Unread 07-10-2013, 04:16 PM   #9
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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Unread 07-10-2013, 04:43 PM   #10
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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Unread 07-10-2013, 04:54 PM   #11
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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Unread 03-13-2014, 09:10 PM   #12
70worm
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Looks like a 4bbl ford carb
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