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.

With that much fuel through it you should see max rpm out of it! They may have toned down the compression with the new piston but why....
I would do a basic check of the whole motor. Start with the valve lash. You should check this every few hours of run time. Sounds like you have enough fuel through the motor to have checked this a couple of times. This is one of the main reasons for performance degradation.
Check all bolts for tightness. Pressure loss through the crankcase is also a cause.
Double check the regulator for correct installation and holes. Even the manufacturers can screw up.

Hope she feels better soon!

Deptydog,
what is valve lash. Never heard that term before.

I did check the valves before I installed the motor. They were perfect. I checked all my screws before I installed it, and they were tight.

Like I said. I have about 1/2 gallon thru it. Do I need to flight it some more, and just keep breaking in my engine. And start worry about it after about another 1/2 gallon are so.

I was thinking about freshness of fuel. this just is about 3 months old. I have about 1 tank or so left in the jug. I am picking me up some fresh fuel this week for the weekend. So maybe this might help. by the way I am running byron 20/20

Y-S 63's usually do 10,500 with 30 heli and APC 13-6 at lower altitudes.

Enjoy,

Jim

Wayne,
But I haven't moved. I was getting 11,400 with same prop and fuel from the same jug before I started having problems.

FWIW:

I get over 11,000 easily with the APC 13x6 on Wildcat 20/20 and an OS F plug.

Chuck

Waa it by any chance cooler weather before when you were getting more power? Mine always seem amazingly powerful the first nice cool fall day after a hot summer of flying! Also, My YS .63 took more than 1/2 gallon of fuel to fully break in and make max power. I might just be that the new piston and ring need to break in a bit more..

Lee