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Back firing | Forum

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Mkbakker Member
Mkbakker May 6 '16, 22:07
Anyone have any idea how to solve my back firing problem. It is extremely loud when I down gear or when I hit the gas hard and led go of the gas. It's a CJ7 with a 258, I just put a brand new Weber carb in it. I set the timing to 8 degrees, my vacuum is at 20 and I have played with the carb adjustment, it's idling beautiful at 700 rpm. Any suggestions would be great, I'm scratching my head now.
#1
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kurplunk Prez
kurplunk May 7 '16, 07:03
Do you know what the condition of your exhaust manifold is in? Maybe it has a leak? It would be a pain in the butt to change those rusty bolts, but maybe you need a new gasket? My understanding with this is if the exhaust manifold gasket has a leak, when rich (unspent) fuel mixture collects exhaust system and is leaned out by the air leak, this raw mixture can become combustible and backfire. 


I also looked online a bit and it seems some people have this issue because of the float in their carb is set too low... just another thought?
link -> Backfiring during deceleration

#2
kurplunk Prez
kurplunk May 7 '16, 07:13
Leave it to a CJ owner to leave the first how to question.. hahah :) 
#3
Mkbakker Member
Mkbakker May 8 '16, 15:40
That's funny. It started to happen after I installed a brand new Weber carb. According my plugs for im running very lean. My choke doesn't seem to want to stay open, that's my first plan of attack. I tried to set my timing but it's hard to see the mark with my timing light.
#4
kurplunk Prez
kurplunk May 9 '16, 12:40
Yeah the choke could definitely cause that issue. Let me know what you find out with some more investigating.
#5
kurplunk Prez
kurplunk May 11 '16, 06:07
Did you solve the problem?
#6
Mkbakker Member
Mkbakker May 21 '16, 17:47
I think I did, took the vacuum hose off the PCV valve and it stopped back firing so I put a filter on the second hose on the PCV valve and so far so good
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#7
kurplunk Prez
kurplunk May 30 '16, 07:22
Great to hear Mkbakker, that's an easy fix! Hope it's still working for you
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