Having used the YS-Zero this season here is my findings / thoughts:

· The engine produces max power on a very narrow needle range setting, compared with using fuel containing 20-30% nitro. Having said that, the power produced is enough for both P19 and F19. A get around 7000 rpm on APC 20x10.5 PNC, slight less on the APC 20.5x10 PNC.

· I use 10% oil (Molsyn 80K), the rest is methanol. For temperature mid 20s C and above, I find the best method to have a reliable engine is the cool down the fuel. As the attached graph shows the vapour pressure of pure methanol increase very rapidly, the 10% oil in the methanol will raise this curve somewhat.
The problem is in verticals like a stall turn, due to gravity the fuel pressure at the pump inlet drops, assume the distance between the tank and engine is 0.5 m, the pressure drop (approx.) is rho*g*h = 800*9.81*0.5 = 4 kPa = 0.04 bar. In addition the pressure drop across the clunk and the friction. In this flight condition (stall turn) it easy to get a vapour lock.
In this respect going back to the days with crankcase pressure in the tank would be a good idea.

· Measuring the pump pressure at idle I ended up at slightly less than 1 bar (0.96 +/- 0.04). It is possible to get the engine to run at a wide range of different pump pressure settings, but in this case it will not run properly at all throttle settings. Initially I had it at 0.8 bar, however, much less power at midrange.

· To obtain a good idle and transition the cam bearing need to be in a very good condition, more critical than running with a lot of nitro. Personally I would prefer cam bearings with a higher load capacity / stiffness. Compared with the non-DZ engine the load on these bearings have increased.

· Running cost very low, compared to any other power source.

On my engines only the piston is changed for the standard nitro version. For a “genuine” Zero, Yamada may have introduced additional changes, e.g. the carburettor body with throttle has a different part number compared with the non-Zero version.