still have a slow cranking 100
 

So I cleaned up the ground on the 100, charged up the battery and put the good starter generator on and still cranks slow. I then put the compression tester on it. My 100 has 90 psi and my 108 has 60 psi and I know my 108 doesn't have any problems

So is the auto decompresion messed up on my 100 or is it an early one without decompresion? The serial number of the tractor is 107083

Just a guess but maybe the problem is with the compression release mechanism.
You will either have to pull the carb and remove the breather cover to see if the exhaust valve is popping up a little on the compression stroke or the head will have to come off to see it.

Nick,
If it cranks then stops at a point then cranks around again to the same point. It the ARC like previously mentioned.

I have the same problem with my 149. I have been searching here and the 'net for good pictures of those little springs and how to install them just so I can have an idea of what I am getting into before I start taking things apart. Does anybody have pictures?

slow cranking
 

i had this problem ,and it was the spring on the c/r ,i pulled the spark plug and rolled the engine over ,and i could hear the c/r click ,i was able to change the spring from the out side , of my 125 ,i did need to lift the engine up to clear the cam cover ,and be sure to tie a string on the spring ,you don,t want to pull the pan .David

It could be possible that your exhaust valve is out of adjustment. I had a 107 that cranked hard...the valve was way too loose. Tightened it to specs, turns over good now.