Perhaps someone can offer a tip or two. The motor is brand new and was bench run - about 1/2 a gallon pretty rich with cool down periods in between 11 oz tank fulls. its now on the airframe and has dead sticked on me once. I decided to tune it better for the next flight. I have managed to get a great transition from idle - which is really slow if I want to a max of 9100 rpm with a 16x6 APC on 5%nitro 20% castor fuel. The problem is the mid range - from about 4500 rpm - if its left around this setting or even up to 6000 rpm it starts running richer and richer until it eventually bogs when you open the throttle and sometimes cuts. This is waht happened on flight one with a far richer main needle setting. The plane was a brand new F90 and I didnt want to rip the wings off so I throttled back and after a few mins she styarted sounding really rich and she cut. Any ideas, anyone[]?

More running time & a bit leaner on the low-speed needle.

You don't really need to run it that sloopy rich with all that castor, you can't
hurt the engine....lean it out and get it running properly....

....the engine will take care of it's self the more you run it.

FBD.

Both your responses are good.

The ring will not seat properly unless run at full load momentarily, then idled for a bit, then full load again, back and forth. The ring will be fully seated in five (or ten maximum) minutes doing this. Ringed engines aren't like the tapered bore, or lapped piston engines. Each one has its best way of running in.

The ring needs pressure against the cylinder wall to seat, more pressure than just its natural spring. The combustion pressure gets behind the ring and pushes it out firmly, leading to its seating.

Full load gives it the seating pressure, then a momentary idle lets it cool a bit and get more oil on the rubbing face, then hit it again.

Once the ring has fully seated your problem should go away.

Bill.