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96 chevy 4.3 backfires

my truck is back fireing when its warm new fuel pump, plugs and wires and new cap and rotor. runs fine when its cold.

Backfiring through the intake? Or, the tailpipe?
Common causes are timing is off, or mixture is too lean, or valves sticking. Perform a vacuum test. Here’s how: http://www.international-auto.com/fiat-lancia-tips-on-reading-gauges/tips-on-reading-gauges-vacuum-gauges.cfm and this: http://www.secondchancegarage.com/public/186.cfm

http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c152800bfe20

Then the next thing to check is worn spider injector assembly. Here’s what it looks like and where it’s located.

Tester