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Old 02-07-2013, 08:56 PM
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huge backfires through carb

I recently decided to put together a sbc I had laying around. I used a lightly used crate short block and put 2.02 heads on it. Cant get it to run and I am getting the loudest backfires I have ever heard! Ive checked my ignition timing and firing order on my hei distributor numerous times and they are correct. I know im not 180 off because I found tdc with the valve cover off and verified I was on the compression stroke with my finger in the plug hole. Ive checked compression and they are at 150 in all cylinders. When I take the carb off I noticed there was a lot of standing fuel in the intake. Swaped my Holley for a Edelbrock off a running vehicle and I still have the same problem. I am going crazy over here Can someone please help me??
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Old 02-07-2013, 09:07 PM
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If the ignition wires are in the correct firing order is it possible that the distributor is off 1 tooth, thereby throwing the firing order off. It sounds like each cylinder is not burning the fuel causing the backup in the intake manifold. Or possibly the wrong plugs in the heads?
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Old 02-07-2013, 09:09 PM
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Are you suggesting a hotter plug? Im sure Im not a tooth off!
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Old 02-07-2013, 09:34 PM
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If your positive the timing is correct, then that leaves a few things to check.
For starters I'd check the voltage going to the HEI, it must get a 12 volt signal. If it gets less it will run, but backfiring and running like crap will be the result. Next I would check the spark, if the spark is blue it's good, if it's yellow it's weak. Next check the valve adjustment very carefully, if any are too tight it will cause this same thing. Also when you put this engine together did you match the balancer to the timing tab? If you used a 12 o'clock balancer and a 2 o'clock tab then the timing is way off.
If all these things check out good then the last thing I would suspect is the timing is off on the chain.
You also may want to check and make sure it doesn't have a major vacuum leak.
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Old 02-07-2013, 10:07 PM
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Quote:
Originally Posted by DoubleVision View Post
If your positive the timing is correct, then that leaves a few things to check.
For starters I'd check the voltage going to the HEI, it must get a 12 volt signal. If it gets less it will run, but backfiring and running like crap will be the result. Next I would check the spark, if the spark is blue it's good, if it's yellow it's weak. Next check the valve adjustment very carefully, if any are too tight it will cause this same thing. Also when you put this engine together did you match the balancer to the timing tab? If you used a 12 o'clock balancer and a 2 o'clock tab then the timing is way off.
If all these things check out good then the last thing I would suspect is the timing is off on the chain.
You also may want to check and make sure it doesn't have a major vacuum leak.
I am running a wire straight from the battery to the dist. I also purchased new wires, plugs, cap, rotor, and coil. My latest suspicion is my heads. Is it possible I am leaking air from the compression stroke through the intake valve? (thought that would explain the excessive fuel in the intake) I did not use valve grinding compound and lapping tool when installing my valves. Does my even compression rule this out?
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Old 02-07-2013, 11:49 PM
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Got her licked!! Im a idiot! Set my cam gear at 6 o'clock and crank at 12 with #1 at tdc. Cam is 180 off. Thanks to all who responded
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Old 02-07-2013, 11:53 PM
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Quote:
Originally Posted by pilona42 View Post
Got her licked!! Im a idiot! Set my cam gear at 6 o'clock and crank at 12 with #1 at tdc. Cam is 180 off. Thanks to all who responded
Just reset the distributor 180 degrees from where it is. That will put everything as it should be, no need to remove the cam!
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