Backfiring while driving

[1972GMCsierra4x4]

So my old truck likes to backfire once in a while while I'm driving it. I rebuilt my carb a couple of weeks ago, and when the choke is set to the factory spot, the truck will occasionally backfire when I'm accelerating. The carb is an 600cfm edelbrock 1406 with electronic choke. My engine is a 350 with 62cc heads and a compression ratio of about 10:1 (if my math is right.) If I set my choke to very rich the problem is solved and my truck runs great. I need to know though if this could be a more serious problem or if I'm just running the wrong size of carburetor.

[tarafied1]

backfiring under light load or accelerating is a sign of a lean condition. If the choke helps that also indicates the carb is lean because the choke basically richens the mixture by limiting the air intake. I'm not too familiar with the Edelbrock. A 600 should be plenty for a mild 350. I'm running a 600 Holley on mine. On a Holley you can change the main jet size and/or the power valve. Not sure how too adjust the Edelbrock though. Most people say you just bolt 'em on and go. You can fine tune a Holley or one of the many copies (Demon, BG, Quick Fuel, etc.). I think the Edelbrock is a copy of the old Carter AFB

[1972GMCsierra4x4]

Yeah with the edelbrock it is a bolt and go carb. As rich as I'm running my 600 to get good performance I think I may need to go to a 750

[tarafied1]

how was it running before you rebuilt it? Did it do the same thing?
Where is the timing set? vacuum advance and/or mechanical advance working?

[1972GMCsierra4x4]

The truck ran the same way before I rebuilt it, less often during the hotter-than-all-get-out summers we have here in Kansas. Timing is set at 6 degrees bdtc (factory for 1972). The vacuum advance on my pertronix distributor is good also.

[tarafied1]

Originally Posted by 1972GMCsierra4x4

The truck ran the same way before I rebuilt it, less often during the hotter-than-all-get-out summers we have here in Kansas. Timing is set at 6 degrees bdtc (factory for 1972). The vacuum advance on my pertronix distributor is good also.

you might try advancing it some, with high compression and today's fuel it may like a little more timing.

[1972GMCsierra4x4]

Alright. Thanks a bunch for your help!

[tarafied1]

sure, I'd try a little at a time but it's pretty easy and you can put it back if it doesn't help. I have a late 70's HEI distributor in mine and it likes about 12 BTDC