Picked up an old timberwolf a while back and ran 10w40 like I had always done in my old Honda's and Grizzly. Finally downloaded a manual and it said 10w30.
It has run fine, but wondered if the "splash" lubrication needed the lighter oil weight? I have generally done what he manuals recommend, and do not know if it really matters.

 

I don't think it matters much. It is mostly for heat dissipation. 10-40 will give you a wider heat range however, 10-30 may be a better lubricant. If heat doesn't seem to be an issue then chances are you will be fine. I would use the 10-30.
If you visit the Amsoil web site they have some good articles on oil.

 

Doesn't the manual give you a chart with several different oils for different ambient temperatures????? Are they suggesting 10W30 as an all weather oil????

In hot summer weather, I would think you would want at least 10W40, if not even 20W50 if you are in the very hot southern states.

 

They gave 5W-30 for under freezing and 10w 30 as the all around and a straight 40W as an option over 60 degrees. I just put some 10w30 synthetic in the T-wolf and Beartracker to see what goes. The kids beat them around the property. I have always run 5W-40 Rotella. I was just curious, as it was lighter for an air cooled bike than I was used to.