RE: rossi 53..UT pylon muffler.. prop jet... what prop?
That guy with a purple patriot had REAL good results with a larger prop. I would go back and read what he did...
The engine is great, that muffler is great, but keeping it in the power band as Mike mentioned is the key. That engine does not like to spin 18K, bigger prop. lower RPM's...
Cheers!