81 kz1100a1 backfiring

After researching on this site I realized that It was twisted. I’ve done lots of motor work but this bike was given to me. Which made me tear it apart. I’m am currently looking at the cases apart and crank laying on the bench. Gonna get this beast running

Also I have another kz 1000 motor in the house which is chain drive serviced in 2019 sitting there. Debating whether or not to swap the final drive to shaft or order a used crank. I hate to tear the good motor apart.