started one day truck runs fine i do basic tune up,replace distributor cap ,rotor,plugs, and wires and a accel super coil. .truck jumped to high ideling moved timeimg back a hair truck is hard to start somedays ,then runs fine all of sudden i thought bad gas it was running crap drained fresh 91 octane. Driveing then starts backfire through carb and jerking need help ,order a new carb .waiting for delivery in morning. What else could it be. Be all this it was running fine

 

If you are getting a backfire through carb the timing is to far advanced. Put a timing light on it and see what it's set at.