As you may have read, I have been flying an OS 1.40RX. The engine runs very well on a 16 x 14 APC and an OS "F" plug using the supplied OS pipe and header. This combination gives 8,400 rpm on 15% Coolpower sport fuel. Now if that was not enough to keep anyone happy, you can now add the YS1.40FZ to the equation. This latest acquisition was fitted to my Ariel and after one tank on the ground it was deemed good enough to fly by impatient onlookers. Running rich with a 15 x 13N the plane would give pure vertical. (Pure vertical is when a plane gives a constant roll rate with the same aileron deflection--thus indicating no loss of air speed as the plane climbs.) I can hardly wait to see the effect upon designs that these engines will give.
For all of you YS fans out there, here are a few observations: - 4 ounces lighter than my YS1.20AC; 2.8 ounces lighter than my YS1.20SC. - Same type of carb. as the SC although barrel and body have different part numbers. Transition adjustment screw is in barrel body, same as the SC. - They have changed the pressure feed set up so that it loops from the front of the crankcase to the rear non-atmospheric chamber of the carb. Then there is a second nipple that feeds the tank with pressure. This nipple comes from the same non-atmospheric chamber. The guess is that this will reduce the tank pressure and help the idle.
- Head is similar to the SC in that it utilizes the rocker box cover as an air-chamber. Valves are the same as the SC. Head also has less material in combustion chamber. Head bolts are smaller diameter like the backplate bolts.
- Rear carb and rotor assembly is held on with smaller bolts equal to the small ones used on the 120 carb.
- Crankshaft does not have ring(s) to keep fuel off main bearing.
- Con-rod is cast and of I-beam design.
- Saddle on outside of crankcase shows the machined depth inside for the longer con-rod swing.
- Same bearings, rear and front, as the SC.
- Rotors are same part #.
- Cam is different part #?
- Taper fitting on Prop. thrust washer instead of Woodruff- key
- Brand new needle design. Ratchet moves with needle!
