I have run about 12 oz of fuel through mine, the last 4 oz in one run. This fuel was 25% castor, 30% ether, and 45% kerosene. I don't think the engine is completely broken in, although it ran steadly and did not overcompress whilst running out 4 oz of fuel. It did not hand start readily, perhaps due to the low ether content, but started instantly with a starter.
Two complaints. The ferrous contapiston is in a ferrous button head. That is fine, but the fit of the contrapiston was too tight. The contrapiston would stick and compression could not be backed off once the engine was running--essentially a fixed compression engine. I worked on it a little and got it better. That fit is tricky and sticking contrapistons in diesels are not uncommon. Better too tight than too loose, I suppose.
Secondly, the NVA appears to be the same as for some larger engine and the clicks are too coarse. One click in from running setting is too lean, one click out is too rich. I will eventually replace it with an ST NVA.
The best consistant RPM with a 7 x 5 APC was 11,500-11,700. On warming up, it would momentarily go above 12,000, but I could not adjust it to hold this RPM. I would guess with more fiddling and running time, it will probably hold 12,500 or so.
In comparison: April 1996 Aeromodeller review of the PAW 09 CT Blue Head plain bearing diesel: weight, no muffler, 4.75 oz. APC 7 x 6 12,200, APC 7 x 4 14,900.
May 1963 Aeromodeller review of Cox TD 09, no muffler, weight 2.75 oz, 30% nitro, 7 x 4 Top Flite 15,500.
Jim Thomerson