OS81 FSa Pumped Main needle sensitivity
Just a quick "is there anything obvious to check" question.
Engine is a brand new OS81 FSa (pumped), now with 8x12minute runs on it. First three runs were on a bench following recommended running in process. Fuel is 16% synthetic/2% castor & 5% nitro. I'm an experienced user with many four strokes (OS, Saito, YS).
From the start, the engine has shown extreme main needle sensitivity. Leaned out somewhat and four-stroking nicely it produces good power (13x7APC), but literally one or two clicks rich from here and it goes so rich as to be unusable. During running in this problem was so pronounced that the glow igniter had to be left connected.
In the air it runs OK leaned out but is unreliable, and if allowed to go marginally rich in the lowrange or midrange it can be impossible to clear.
No fuel leaks anywhere on the motor, and behaviour is the same on the bench as in the airframe (Rapture 50).
My only other pumped OS is a 120 and that is as good as gold.
Any thoughts appreciated,