I should probably read more of your post before I start slinging out questions...We've had no problems running the stock connecting rod up to 6000 rpm. Frequent oil changes with a good oil are very important. As mentioned earlier in this thread, the stock rod is metal to metal with the crank journal which is fine for a motor running at no more than 3600 rpm.
Once we modify these motors so they are capable of over 6000 rpm we definitely use a billet connecting rod. The billet rods have bearings like car engines do. When you place a billet rod side by side with a stock rod, the stock rod looks like it was built by caveman. The billet rods are very high quality.
Another good reason to use a billet rod in this application (with the engine sitting at 90 degrees) is because instead of having a simple dipper, it has a scooper. The scooper is cupped and actually scoops up oil and slings it into the cylinder.
In our go karts we run the engines on a 15 degree motor mount. I have never seen one mounted at about 90 degrees until I saw Lurkers bike. Hopefully Lurker is putting some miles on his bike and we can get some feedback on how well the oiling system (dipper) is working. Glad to see so many others going the same route with the clone motor.
The stock connecting rod is the weakest link in the 6.5hp clone motor. As I said above we had no problems with the stock rod up to 6000 rpm as long as we changed the oil frequently. The stock flywheel would be the next weak link. When you remove the governor and spin these engines beyond 3600 rpm the magnet can separate itself from the flywheel. The magnet is held in place with epoxy and a screw. Our aluminum flywheels have magnets that are either cast into the flywheel or held in with roll pins. These magnets will not separate from the flywheel. The aluminum flywheels are much lighter than stock too. Reducing that rotating mass is good for almost 1hp. That's a big gain in power considering the engine only produces 6.5hp.
So in AGK's opinion, what are your thoughts in notching for oil drain like cobra did? See the comment on bearings so that question is covered, as well as flywheel and connecting rod, and carb. Can I get all those parts direct from AGK? you take paypal at all?