Yes, i have had the same issue as you have and went through the exercise of running Seafoam through the engine with no results. The previous owner had replaced the starter but it would only spin and not turn the engine. Bump starting was the routine for a while.
I went through the exercise of pulling the engine so that I could get at the sprag clutch and found that everything inside was clean as a whistle.
Now with the back cover off, it was easy to watch what was happening inside when the starter turned. In my case nothing turned inside, neither the starter gear nor the chain moved, only the starter internal gears were spinning!
I wish Honda would have made an access hole near the starter gear as an easy way to position the starter gear when reinstalling a starter motor.
Dissasembly of the starter motor revealed the problem. Cheap plastic outer ring gear that was held in place by a pin on the outer edge of the plastic. So when the starter turned the chain, the sprag clutch engaged and then the plastic ring gear rotated out of position about 20 degrees causing the planetary gears to bind and the armature to spin freely. This was clearly not an OEM product.
Hence a used replacement OEM starter was found on ebay and installed. Now the engine will turn over when the starter is called to action.
Gee I wish I had of gone the easy route first. Well, removing the starter with the engine in place is not an easy chore but it is far easier then pulling the engine.
I would say to try what the other posts are saying about using Seafom, it is quick and easy and will clean your engine for you and may solve your problem as it has done so for other riders. Next check the starter itself ( see the excellent post about starter rebuilds ) and if possible have it tested under load. Last resort .......... pull the engine.