Thanks mrctattoo!
Questions:
---Do you have your engine inverted?
---Do you have fueling problems...ie fuel tank too high, etc?
---Does the CG come out to your satisfaction with the "heavier" OS.91?
---What prop are you using with your OS?
---What size spinner?
---Did you need to alter the right thrust from stock?

Thanks for any info. I'm glad someone is using on OS.91!