What you're experiencing is normal. Starting an engine for the first time in a new flying season will require some re-adjustments. Some engines will have to be re-tuned every session at the field while others seem happy with one constant setting.

In regard to your Max, it doesn't sound like you're tuning the engine properly. Set the needle valve for maximum RPM and then back it out 15-30 degrees. While other engines will run fine with a lean setting, OS engines will not run reliably tuned for maximum RPMs. Your prop and fuel are OK.

Ciao,

Eagle Al