Hi Troy, I have a quick question for you. I just recieved my YS91ac back from the service center about a month ago and flew it yesturday on a Fliton Inspire. I set the high needle at about 2 turns open which may be a little rich, but no one else was at the field to hold the airplane to use a tach. Anyway, it was running fine for about 8 minutes of flight with a lot of transitions as it was the maiden flight and I was just testing it out. I brought it over the runway to do a trial pattern to set up for landing, as it came in I reduced power from about 1/4 to idle in order to simulate a landing, as I re applied power it backfired tossing the prop and spinner (I was not using a lock nut due to a FAI style short spinner, I now have an Ultimate type spinner as I lost the first when it came off so I will be using a lock nut now). I am not very familiar with the YS engine, but it did suprise me in that is kicked the prop off during transition, it had not reached full power. I did not mess with any of the settings from the service center other then the high end, do I need to back the pressure regulator screw out? In other words would this be an indication of too lean in the middle, or does the main needle need to be richened up? I am using a YS 20/20 fuel. Thanks for the help.