Odd ? I have a KA100 OTK Mercury R. I noticed our rear axle doesn’t spin as long as everyone else’s. If i take the chain off the axle spins forever. With the chain on its spins but for a very short time. The chain is not to tight and there is about 5/8 under 3/4 of play. I took the side cover off the engine popped off the clutch and the bearing, greased the bearing and put it back together. Does the same thing. Engine was brand new and we only have a few months of practice weekends on it. Doesn’t matter the rear sprocket size or the chain size. Same result and i have the laser to line up the sprockets. AM i missing something or is there just no need for concern?
You using an O-ring chain?
Probably no need for concern. Depending on lube, temp, chain age etc. it can affect how freely it spins. I wouldn’t worry too much about it.
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D.I.D #219 HTZ SDH Chain, says non O-Ring
I didn’t know if the lack of free spinning had any bearing on performance/speed/ etc, and was just a little concerned 
If you spin it slowly does it bind at a specific place?
I had the same problem with an old chain. Apparently it was stretched unevenly. Changed the chain, the problem was solved.
I have switched chains. Brand new because we went to an 80tooth and the 104 i had was too short. Same thing. When i spin the tire hard it only does 3.5 rotations. When i spin slowly its feels fine.
Make sure the gears are aligned, the chain is not too tight and the chain is lubricated.
Some O-ring chains spin freer than others. Don’t be too concerned.
10-4 all of those are good on my end. Thank you for the help
Does the clutch drum spin freely without the chain? If not, sometimes there isn’t enough end play and the clutch drum drags on the thrust washer, which doesn’t matter because the clutch is locked up on the track. It is also possible that shoes are dragging, which could be a problem.
I will check that out and follow up. ty