What would cause a carb to basically back fire? I have a 1987 dodge dakota 3.9L V6 with very few miles for it's age. I was driving it one day on the highway and it started doing this. I adjusted the timing, replaced plugs, wires, distributor cap, rotor button, and rechecked the timing but it won't stop. I'm thinking I need to check my valve lash, but I want to be sure that's what the problem is before I tear into the engine again.

Backfiring through the carb (spitting or coughing) usually occurs in the morning when a carb's air/fuel mixture is a bit too lean. This usually goes away once the engine warms-up. It is also commonly caused by the accelerator pump inthe carb not squirting enough fuel before the main jets start working. If you spit the instant you blip the throttle it is probably the accelerator pump in the carb not working, plugged up or out of adjustment................................... As with backfiring, coughing or spitting can also be caused by a bad ignition system, such as cross firing (when two spark plug wires are touching and arcing together), which sends a spark to a cylinder that has the intake valve open. When that plug sparks out of turn, it lights the fuel in the cylinder and the pressure has to go somewhere... so if the intake valve is open, it goes right back up through the intake manifold and out the carb with a "spit" and sometimes even a flame....................... Ref.: http://www.badasscars.com/index.cfm/page/ptype=product/product_id=95/prd95.htm

Have you tried changing the fuel pressure regulator