22Racer is right on with the idle gap. I suspect your idle gap is too wide, meaning you are running very rich on the bottom and too lean on the top.
Motor performs ok, but gets hot towards the end of the tank, and will kill plugs quite often.
Set idle gap to .7 - 1mm as suggested. Flush HSN and set LSN 1.5 turns in. Warm up motor and turn LSN in far enough to get good pinch test or nice sharp acceleration off the mark and a steady idle. That should be right on tune or close to it. Maybe 2 hours more in on the HSN but not much more. Also remember the Go engines need only very small needle adjustments. 1 - 2 hours can be too far. They are very sensitive when close to a good tune. The Go's like a fairly lean bottom end and a rich top end (with the long LSN). You can tell if you have the long LSN as it stays in the spray bar right up to full throttle. The short LSN pulls out of the spray bar at around 1/4 to 1/2 throttle.
Like 22 racer also said, don't stop your motor by plugging the exhaust as this WILL blow plugs. Best way IMO is to stop flywheel. Pinching off fuel line works but runs your motor lean all the time, then you try and start it with no fuel in the motor or fuel line which is not good for it either.