1994 Chevy van, why is it backfiring?

[Ivan Cornejo]

I have a 1994 Chevy van g20 with a 4.3l. I had the timing done last week, took it on the highway and when it hits about 70 mph she starts backfiring. What could it be?

 

[herm0016]

Vacume advance may not be hooked back up.

 

[RLGL]

Have the timing checked, might be set wrong. With a stock system, once the timing is set correctly , it should never change unless something is worn or failed.

 

[ondma]

Could be many things. I had an older car that backfired simply because the spark plugs faulty.