I have a YS 63FZ. I bought it new. I had 3 1/2 gallons thru it and started having problems. So i sent it back into YS to get it fixed. They fixed my regulator spring problems, and replace my piston,(because they updated pistons on this engine)

My warranty runs out on Sept. 28. OK know here is my questions.

Before I sent the motor in and before I was having problems. I was getting 11,500 PEAK Rpms w/ APC 13x6. I would set this motor to fly at 10,800-10,900.

Now that my motor is fixed I have now ran 1/2 gallons of same fuel thru it.(Last 1/2 gallon of jub before I sent my motor.) This is the same 13x6 prop. My RPMs figures are 10,400 PEAK. I set it to fly at 10,000.

Did I loose 1k RPMs because my motor isn't broken in yet, since I got the new piston.

My fuel filter is pretty clean. Before next flight, I am going to replace it.

My throttle transition was perfect before. Now my throttle transition is not so great. I sounds like its surging a little if I run it at about 1/3 for a min. or 2.

Any suggestions on why I lost 1000RPMs.

Do I need to calm down, and just fly it and get some more fuel ran thru it.

Before I was having problems, this motor was perfect in everyway. Now is just about average. I want my peformance back. Any pointers are suggestions are greatly appreciated.