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post #1 of (permalink) Old 01-03-2002, 05:12 AM
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Engine backfiring when turned off

I just finished building my CJ5 258. I did a complete rebuild to include HEI, Weber 32/36, Clifford mid Cam, bored .30 over. I'm not sure if the carb is jetted correctly, nor am I very good at figuring out which jets I should be running. The main question that I have is that after about a half hour easy ride yesterday I stopped at the gas station to fill up and right after I turned the key of there was a really loud backfire (much louder than when you are driving and have a backfire) Any help is appreciated.
Thanks Jon

Jon
84 Toy,73 CJ5,90 RM125
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post #2 of (permalink) Old 01-03-2002, 06:56 AM
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Re: Engine backfiring when turned off

Well I don't know about Weber carbs but usually the carb is useing the idle circuit(engine is idling) when you shut the engine off. To backfire on shutdown means it is running lean in the idle circuit or actual timing is way off. If the weber has idle screws, have you messed with them? With my non-comp. BBD I went buy tune-up specs but also used a vacuum gauge for highest pull, evenly adjusting both screws. Good Luck.

Huh?
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post #3 of (permalink) Old 01-03-2002, 08:56 AM
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Re: Engine backfiring when turned off

Alot of these type problems occur when the idle is set to high. Try backing off on the idle screws, and set the idle rpm lower. Worked for me.
Good luck.

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post #4 of (permalink) Old 01-03-2002, 04:30 PM
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Re: Engine backfiring when turned off

Thanks, I had a problem with my throttle sticking (new throttle cable, and some wiring that was hanging)so I'll try that first. What are people setting their idle at? I had mine at 650-700 with the timing set to 8*. Thanks for the help.

Jon
84 Toy,73 CJ5,90 RM125
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post #5 of (permalink) Old 01-03-2002, 05:12 PM
 
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Re: Engine backfiring when turned off

He's probably got the rotor phasing way off when he installed.
The teeth are 60 degrees distributor degrees apart on a GM HEI, and if you don't clock the gear correctly, the rotor nose will be anywhere up to 30 degrees out of alignment with the spark plug wire terminals.

Without a power relay and proper size wiring, the HEI is starved for current.

You also have to contend with the fact that a good portion of the guys that do the distributor change to an GM HEI get the distributor in 180 degrees out anyway...
One thing about a I-6, it runs nearly as well with the distributor in 180 degrees out as it does in correctly, just some power loss and some backfiring...

If it 'Backfired' through the air cleaner, it's probably a fuel problem.
If it 'Backfired' through the exhaust pipes, it almost always ignition.

So many cats, so few recipes...
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post #6 of (permalink) Old 01-04-2002, 04:55 AM
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Re: Engine backfiring when turned off / weber 40?

Thanks TeamRush, but I think that I have found the problem. I have a sizeable fuel/intake leak at the carb to manifold gasket. And yes I set up my HEI 180* off to begin with (a long time ago) and the engine did not run at all. Just to clarify this problem only happens upon shutdown after about 1/2 to 1 hours worth of medium driving. I still think that there is a jetting problem, but that will have to wait until after the gasket fix. BTW is anyone running a weber 40mm duel carb I have one that is not being used and was told it would be better suited for this type of application.

Jon
84 Toy,73 CJ5,90 RM125
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