Carb Backfiring. Timing???? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-19-2010, 11:49 PM
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Carb Backfiring. Timing????

i have recently replaced the lifters and timing chain on my chevy 350, and i am positive i installed the timing chain correctly, but not sure if i adjusted the valves correctly. I am also sure that i have installed the distributor correctly to since i have checked it about 5 times so far. Now when i crank the engine over it backfires out of the carb a lot. Any ideas on what it could be??? i also know that the card is sealed good to the intake too.

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Old 08-20-2010, 04:24 AM
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If you're sure it's not cam or ignition timing, it's probably valves. Assuming it's a hydraulic lifter cam, you need to set the lash at zero plus half a turn.

See pg 4 of Comp Cams installation manual for valve adjustment procedures

Give it a try, if that doesn't work it could be a stuck valve or something I'm not thinking of.
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Old 08-20-2010, 06:31 AM
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This should help with distributor issues: Distributor Installation: Get it dead on the 1st time...
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Old 08-20-2010, 03:06 PM
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okay so somehow i had the disrtibutor 180 degrees off, now it runs. but, i do have a sporadic knocking sound. it isnt all the time just randomly and when i rev it up it quits. it sounds like lower end but i didnt touch the lower end and it was fine before i replaced the lifters and timing chain. it sounds like someone hitting the oil pan or valve covers somewhat hard with a ball peen hammer. any ideas??? could it just be a rattle, like the oil pickup hitting the pan??? or something major???
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Old 08-20-2010, 05:34 PM
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Loose torque converter or flexplate bolts and/or a cracked flexplate will often sound pretty similar.
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Old 08-20-2010, 06:08 PM
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Knock Knock

Quote:
Originally Posted by Rickracer
Loose torque converter or flexplate bolts and/or a cracked flexplate will often sound pretty similar.
My Grandfather use to "Don't let coincidence beat you". It's natural to assume a problem is associated with work you've been doing and often is, but I wouldn't discount a converter bolt or whatever else. Lets just hope nothing got into the bottom when the intake was off. I'm sure that it isn't related to antifreeze getting to the oil, because you drained it first and then changed the oil after you buttoned it up.

Still running the original cam?
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Old 08-23-2010, 01:45 PM
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i checked the flexplate, since it's a stick, and its not cracked or loose. and i am 100 percent positive nothing got into the oil pan because i had it off, it sounds like a spun rod bearing for sure now because i can hear the piston slapping the head all the time now, i only ran the engine for 30 seconds tops, so hopefully the crank is okay. and should i just pull the oil pan on the truck and replace just the bad bearing, or should i pull the engine and replace all bearings???
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Old 08-23-2010, 02:19 PM
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cracked flywheels can be hard to detect. Rap on it with a mallet and you'll hear it if its cracked. I know this works OFF the engine. Im not sure if it works when its attached. Someone here can verify my finely calibrated BFH technique
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Old 08-23-2010, 03:54 PM
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yeah i'll try that.
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Old 08-23-2010, 06:44 PM
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sorry about the unwelcomed sound

Guess I'd pull the pan at least and see what's going on. If I found a bad bearing, I would have a tendancy to go buy a crank kit for just over a hundred and avoid the problem. If you have a bad rod bearing you may have a bad rod. Not unusual to swap out the crank kit with the engine flipped over and the heads still on, but I'd want to know why it went. If you find a bad bearing you're likely to find a bad journal also, not round or whatever. Then the roundness and size of the big end of the rod becomes suspect. Get an inside mic and check it.
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Old 09-02-2010, 11:01 AM
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got the engine running mint now, after pulling out a spark plug i found that the tip it had came off ang got into the cyliner. thanks everyone for your advice!!!
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