Remember the adjustment I'm talking about is the small screw that is inside the throttle lever, not the high speed needle adjustment. Its not clear from the pictures that you have access to that screw with the cowl on. Just checking.

Assuming you purchased the engine from a dealer, not second hand, I wouldn't plug the hole. The designer put it there for a reason, and modifying it will probably void the warranty. If you reduce oil flow to the front bearing, you'll greatly shorten the life of your engine.

Brad