Sportsters don’t overheat and misbehave if you are using the right fuel and prop. Mine don’t like much nitro if you’re going to rev it up, but they don’t really like to rev up. They’re timed low and have a high compression ratio. Use a BIG prop and low nitro, and don’t use muffler pressure to the tank. 5% nitro 22% castor and a 13x6 is perfect for the .65. Taking the baffle out gives a bit more power and noise. Set the needle 500rpm rich of peak and you’re good to go.