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post #1 of (permalink) Old 12-03-2000, 02:49 PM
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258 backFIRING through carb

Here's the deal: I just brought home another "abandoned project" an 81 CJ5. The engine was sound, according to the owner, but hasn't been run in at least a year. I got it home and connected a line from the fuel pump to a can of fresh gas. Upon cranking it almost starts, but ends up backfiring through the carb (FIRE) I checked the timimg at cranking speed and its good enough. Do I have a collapsed lifter, a crossfiring wire or what. I ran out of time but will be back on it later tonight. Any ideas? Thanks in advance. Tom

76 CJ5,2.5" lift/Rancho 9000's,258/T-177/D300,HEI,Offy,Locked F&R
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post #2 of (permalink) Old 12-03-2000, 03:28 PM
 
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Re: 258 backFIRING through carb


I had this when I had a four barrel holley on an old camaro. It was fixed with a timing corrections and some minor adjustments on the carb, I think it might have been the intake screw, could be wrong, I watched my buddy do it. But I remember seeing flames out the top of the carb, and it was along thoose lines to fix it.

'74 CJ5/5.9L Holley 4bbl/3spd/31"/not running
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post #3 of (permalink) Old 12-03-2000, 04:17 PM
 
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Re: 258 backFIRING through carb

Timing is off. what it is, try to picture this. The intake valve is still open while the compression stroke is beginning. So this could be a stuck valve, lifter, or even timing mechanical is off. Pull motor to TDC and check marks on pulley.If timing is too far advance it will backfire through tail pipe.

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post #4 of (permalink) Old 12-04-2000, 09:45 AM
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Re: 258 backFIRING through carb

Make sure your plug wires are connected correctly...

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post #5 of (permalink) Old 12-04-2000, 02:39 PM
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Re: 258 backFIRING through carb

OK, the base timing looks good at cranking speed with a timing light, and since the distributor is cam driven, the timing gears should be alright, right? The wires are installed in the correct order, and I can't see a crossfire, but I'm putting plugs and wires on anyway. Next is a compression test and pulling the valve cover. I'm still open to ideas. Tom

76 CJ5 258 w/Clifford/Holley/HEI, 2.5"Lift/Rancho 9000s,T-177/Dana300
post #6 of (permalink) Old 12-04-2000, 02:50 PM
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Re: 258 backFIRING through carb

After you change the plugs and it still does this, check for leaks/float sticking in the carb. If it has been sitting a while the rubber seals sometimes rot out causing gas to just flow into the carb. And gunk can make your float stick shut where no gas will flow. It's obviously getting spark at the correct time because your timing light works.Also verify the choke closes all the way. That's about all I can tell you.. Good luck, I'm sure you'll figure it out...

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post #7 of (permalink) Old 12-04-2000, 05:49 PM
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Re: 258 backFIRING through carb

Moneypit is correct, carb flooding is (soon to be WAS) the problem. After sitting all night with fresh fuel in the bowl it started much better today, but still proceeded to load up, sputter and die. I pumped a 50/50 mix of unleaded and fuel system cleaner into it and have been starting it every half-hour, it keeps getting better and better. Tommorrow I'll pull the venturi cluster and clean the idle tubes, along with an ignition tune-up. Thanks, guys.

76 CJ5,2.5" lift/Rancho 9000's,258/T-177/D300,HEI,Offy,Locked F&R
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