bad back fire HELP PLEASE

[88 comanche man]

I just swapped a 91 H.O engine block and head in too my 88 MJ . I switched the intake and all sensors, distributer and fly wheel . It starts fine and idles normal but has a bad stumble and back fire between 2-3000 rpm blew the muffler in two . Once past that stumble area it works perfect .
WHAT HAS GONE WRONG ??????????:hang:

 

[GrimmJeeper]

are you sure the distributor is in right? sounds like its firing when at least one of the exhaust valves are open.

 

[88 comanche man]

ithink it is fell right in place and rotor was pointing it same direction but may be off a tooth ahead one maybe ?? if you try to drive it normal it back fires bad but if you mash it to the floor it work like its on NOS ???

 

[88 comanche man]

well got it worked out it was the distibutor . we just took out the hold down bolt and started it up then clocked the cap back and forth till it worked properly . then just pulled cap of maked the position and had to move it 2 teeth works perfect now thnx a bunch