I have a Mustang 50 that until today had been run about 1/2 hour, this engine is supposedly a Fuji 50. Now, according to towers info the Fuji 50 should turn a 20x8 prop at between 8,100 and 8,400 rpm, today all I could get with a Zinger 20x8 running on Amoco 93 octane, oil at 25 to 1, recommended for break in, is 7,350. Will it pick up some more rpm as it gets more run time on it, or is that it. I have a Fuji 50 so called muffler on it, it is a big empty can with a 1 inch outlet pipe.

I have owned a couple of these and they are not powerhouses. The regular Zinger is a dud on this engine. Try a 20x8 or 18x10 Pro Zinger or Master Airscrew Classic 18x10 and you will get into the range you describe. After break-in you can expect a couple hundred RPM increase, but not that much.

remember you also running 25:1 for break-in. You will see improvement when you go to the recommended 40:1. and also I would advise against using 93 octane . Just go with your regular unleaded fuel.

I ran a Mustang 50 yesterday after repair..
22-8 Mejzlik 6600
20-10 MA 7200
No muffler, and this one needed rings pretty bad, so a new one should be better....