Hmm. Now that you mention it, the stock plug was a single electrode CR7HS and I put in a new plug, which MAY have been the plug from the ignition coil kit https://www.amazon.com/gp/product/B00EO0RN5M

OR from the carb kit. I had the parts box mixed together. I have a spare orange plug A7TC which may be from the coil kit or the carb kit. Would that stop the top end? It's idling fine and running fine powerband-wise up until that top speed. The plug wouldn't stall out an engine at 30mph though right? if it were running rough or stalling maybe.