91 fullsize blazer backfiring problem
 

My 91 fullsize blazer just got new head gaskets but when started up it backfires like pop corn popping after a few minutes it will stop and truck runs fine any idea why it's popping

It sounds like your timing may be too far advanced for cold start up. What was the timing set to after the head gasket replacement?

I was not the one who set timing on the truck so I couldn't tell u off hand but all specifications came from
my haynes Manuel for that truck