Hi Bax.
I purchased recently a new OS 65 LA for my Extra 40 size plane.
Two days ago i run the first tank of fuel through it.
And until now i have 3 litres through it.
I use 10% nitro all castor oil and the prop is an APC 12x7.
The problem is that today i run another two tanks of fuel and i measured the rpm rangeeak & idle.
Αnd i saw these measurements:

1) Peak: 9510rpm's
2) Idle: 2130 (1st tank) and 2070(2nd tank).

OS manual claims for 16000 rpm.
I know that these rpm's are when the engine unloads but 16000 to 9510 is way too far.
Also i use an A3 glowplug that came with the engine.
Please tell me what i am doing wrong.
Kostas

The 16,000 RPM is the maximum RPM O.S. ran the engine out with some propeller. That is about as high an RPM as you can run the engine before it self-destructs. If you have the engine turning that high, then you will not get the low-end RPM stated in the range. The lower end is the lowest RPM the engine could be made to run with some propeller attached. You will most certainly NOT get both ends of the RPM range at the same time. Also, if you use a propeller suited to most airplanes intended to be flown with that size engine, then you will get an RPM level between 10,000 and 12,000 RPM.

We'd consider a propeller that made the engine turn below 10,000 RPM a bit too large. We'll prop the engine to turn around 12,000 RPM...11 x7 or 12 x 6, or other propeller pitch/diameter combination that gives around 12K.

Yes but OS suggests either a 13x6 or 13x8.
And i am only using an APC 12x7.
7000 rpm below the 16000 is too far away!
Maybe i have a problem somewhere?

O.S. makes propeller suggestions based upon how the engine is used in Japan. The larger propellers make ther engine run very quietly. We use 11-inch propellers to get the egnine to turn up. With proper break-in, you should have no problems. A 12 x 7 prop would be considered a bit large by our standards.

Please remember that we are not O.S. Engines, but the service center for O.S. engines in North America.

So you suggest a prop that is like 11'' diameter and 6'' pitch?
Or like an 11'' diameter and 7'' pitch?
In this case will rpm increase?