1988 Yamaha 4 wheeler slow crank

Question

I am having a serious slow crank on my 4 wheeler.It is so severe that the 4 wheeler will not start anymore. It is a new battery. I have ruled out all electrical problems and replace the starter. I assumed that the problem was mechanical, so pulled the covers off, pulled the timing chain, and then turned the top end and bottom end manually. Neither the top end or bottom end seem to be binding. Not sure what to do from here. Any ideas?