Battery good but no fully charged... I would check the strap that connects the battery to the ground. On the left side of the battery, it should be firmly connected to the subframe.
I second Gunner with checking the starter motor itself - it is basically an easy job to do.
Other more complicated things comming to mind but check those first.
You can help the starter with manual decompression lever - i usually do to prolong the life of the starter sprague. It is also accepted practice to kill the engine with it instead of the kill switch or key.