86 Chevy van w/ bad backfiring

[sagebrush455]

I have a 86 Chevy G20 van with a 350, 4blr carb. Most of the time this van runs just fine, then out of the blue when I go to start it up it backfires real bad. Whats the deal with this, please help.

[automan63]

If it only does it say like during the mornings its posible that you have burnt intake valves.
I would check plugs and wires also.
How many miles are on this engine?