motor swaps for 89 pup

i have an 89 pup an the motors givin me problems. my #1 cylinder keeps fouling up and sum other stuff. wus wonderin if i should rebuild the one i have or buy a new motor. if so, i need to know of any motor swaps that can be done. i've heard of many swaps but i need to talk to someone who has had experience with any swaps. any help is needed.