6v 9n starter will turn engine oner slowly about four times then stop. Try again and dash mounted starter button will get hot and voltage starts dropping till i let off the button. Removed starter and used jumper cables to energize and it spins fine. cleaned electrical and frame connections, swapped starter button, used a screw driver to make sure flywheel was not binding while starter was out. Battery in very good shape. Short in starter while under load? any other thoughts before i send in for rebuild or replace.