Maximus1
Full Access Member
- Joined
- Mar 6, 2017
- Posts
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I have a 57’ Chevy pickup with a 5.3L swap and converted to carburetor with the Edlebrock intake and MSD 6014 control box. It’s got flattop pistons and a Howard’s cam .555 lift 267/276 duration. I’m having a backfire when I floor it from a stop. Holley says it a lean backfire. So they suggest switching discharge nozzles from a 28 to a 31 on primary and from a 31 to a 35 on the secondaries and also changing my power valve from a 6.5 to a 2.5. All of this I have done with no change. Now the air/fuel mixture screw from bottomed out turned out 1-3/4 turns on all four mixture screws. Now I can fatten them to 2-1/2 turns and I still have a slight stumble with a tiny backfire but it’s running so rich that a ton of black smoke is coming out just at idle. It also fouled out three of the spark plugs causing a misfire. All of this has taken place over a day. Anyone have any ideas about how to correct this problem?
