OS 91 SZ No power

[snake007]

I have the OS91 SZ no pump running on muffler pressure with a header tank running Wildcat CY 30% fuel. I have this motor in a Raptor 90 SE with 710 Radix blades. The head is turning about 1850 RPM and I have it set up for +10 to -10 degrees pitch. I have the throttle jocky pro govener. The problem is the motor is not making very much power. It is running real good and smooth but if I push the stick to the full pitch the head loses about 400 RPM and if I add any cyclic on top of that it falls on its face. I started with a viper head with 2 .008 shims and it was even worse. I put the factory head back on and it got a little better. I then took 1 .08 shim out and put a .004 shim back in. I am not sure but that might have made it better but not by much if any. I have the CY MP5 pipe and if you put your finger on the back plate after a flight it becomes very uncomfortable after anout 5 sec.

Anyone have any ideas?

[Kinger]

What gear ratio are you running? If it's 8.27 (white main gear) you are out of the engines power band at that headspeed. Try bumping it up to about 1920.

[snake007]

Thanks alot I will try that. I am runing the 8.27 gear.

[Benj]

I think your engine maybe detonating which will result in reduced power and potential damage to the motor.
Going on what I have found it looks like on 30%nitro fuel you want more shims, around 20thou (eg. 0.020) shimming all up with a OS 91SZ with a Viperhead (so say 2x 0.008 + 1x 0.004). Try that, hopefully that will work better?

Benj

[DavidH]

I would try leaning the main needle a couple of clicks at a time. Sounds to me like the motor is still running rich.
By taking shims out, your raising the compression of the engine. When you do this and the engine ran better, I would think the mixture was too rich. I would put the two .008 shims back under the Viper head and put the head back on the engine. I then would lean the main needle a few clicks at a time till the motor gets noticeable lean. Then back up 3-4 clicks richer and fly the model.

How much experience you have at tuning nitro engines?

David

[Jafa]

What is your idle up throttle curve?

Remember that the TJPro uses the throttle curve for re-emptive power demand predictions
With the throttle jockey pro in my Freya I had to run a very high throttle curve to get good performance
Something like 100 90 80 90 100

Just another thing to consider