jeep keeps backfiring
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jeep keeps backfiring
I bought a 76 jeep cj5 for my wife so we could go 4x4ing together, she convinced me that the 78 ford f-150 hi-boy was "just to big to see everything around me". Granted, she is only 5 feet tall and often had a hard time. Anyway, just felt the need to explain, and on to the problem:
It seems to run very well now, plenty of power, with the exception of two things. It keeps "backfiring" after I release the accelerator at high RPMs while driving (it is a 3 speed), and it diesels when I shut it off. I don't mean a little cough, I mean like it will run until i tap the accelerator. It also seams to run very hot.
This jeep is pretty simple, 258 inline 6, 3 speed, 1 bbl carter carb, no a/c, no ps, no pb, no computer (has ignition module tho). I have rebuilt the carb, set idle to manufaturer spec, set air/fuel by manufacturers spec, replaced spark plugs, wires, dist cap, rotor bug, ignition module, and set timing (after disconecting vacuum to distributor) and checked it repeatedly.
I think the overheating is causing pre-ignition and I am leaning toward the thermostat or the water pump. The upper radiator hose is wire reinforced so I cannot check it by squeezing, but I do see coolant moving in the radiator.
I appreciate any help.
It seems to run very well now, plenty of power, with the exception of two things. It keeps "backfiring" after I release the accelerator at high RPMs while driving (it is a 3 speed), and it diesels when I shut it off. I don't mean a little cough, I mean like it will run until i tap the accelerator. It also seams to run very hot.
This jeep is pretty simple, 258 inline 6, 3 speed, 1 bbl carter carb, no a/c, no ps, no pb, no computer (has ignition module tho). I have rebuilt the carb, set idle to manufaturer spec, set air/fuel by manufacturers spec, replaced spark plugs, wires, dist cap, rotor bug, ignition module, and set timing (after disconecting vacuum to distributor) and checked it repeatedly.
I think the overheating is causing pre-ignition and I am leaning toward the thermostat or the water pump. The upper radiator hose is wire reinforced so I cannot check it by squeezing, but I do see coolant moving in the radiator.
I appreciate any help.
Elder User
Joined: Mar 2005
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From: Cornelius, Oregon
The backfiring on let-off could be caused by a leak in the exhaust. It's pretty normal, my 95 wrangler does the same thing, so does my motorcycle. It's caused by a rich condition when you let off the accelerator, then when it hits the fresh oxygen (due to the leak) in the hot exhaust it spontaneously combusts.
There are many things that could be causing the dieseling after shut off, first I would check the timing, but you say you've already done that. Have you tried retarding it a little and seeing if it still does it? Running the igition too far advanced will also cause it to overheat. Is it hard to start or slugish when cranked over? That is a sure sign of too much advance. What is the advance set at?
When you say it will run until you tap the accellerator, does it immediately shut of, or do you have to pump the accell a little?
There are many things that could be causing the dieseling after shut off, first I would check the timing, but you say you've already done that. Have you tried retarding it a little and seeing if it still does it? Running the igition too far advanced will also cause it to overheat. Is it hard to start or slugish when cranked over? That is a sure sign of too much advance. What is the advance set at?
When you say it will run until you tap the accellerator, does it immediately shut of, or do you have to pump the accell a little?
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A-ha, good call on the exhast leak 
. Found it after 5 min seach. Thanks
As for the timing, I have tried setting it in all the manufacturers designated specs ( 6 - 10 degree BTDC ) and also a couple higher and lower to no avail.
Concerning the accelerator, it is just a tap and it dies, but it will continue dieseling if i leave it alone
.
Thanks for the advice on the exhaust, I didn't know that a leak would have that effect !
. Found it after 5 min seach. ThanksAs for the timing, I have tried setting it in all the manufacturers designated specs ( 6 - 10 degree BTDC ) and also a couple higher and lower to no avail.
Concerning the accelerator, it is just a tap and it dies, but it will continue dieseling if i leave it alone
.Thanks for the advice on the exhaust, I didn't know that a leak would have that effect !
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