You can never use Nova plugs in the engine now that you’ve used an OS plug in it. Just FYI. Next, the ultra hot plug is too hot. You need a medium heat plug in that engine and you need to adjust the carburetor for proper running. It’s likely very rich from the factory and thus loads with fuel and quits. If when you punch the throttle to WOT it cuts out immediately and will die if held there, it’s too lean. If you haven’t adjusted the high speed needle from the setting it had from the box, it’s probably too rich.

Change to a medium heat plug and plan to change fuel to something with less oil in it once it’s got a half gallon through it or so. Or burn up the gallon of 20/14 you have and go to 20/11 or 20/10 after.