YS-63s . . .

A YS 63s is a very high performance four cycle model airplane engine. I got one perhaps two years ago. Installed in cheap plane and about six months ago started to try to fly the plane. YS engines are made by Yamada in Japan. They are the most powerful per cubic inch alcohol fired engines available.

I could not get the engine to run at max RPM - about 12,000 RPM. All it would do was about 8,700. Not satisfactory at all. At about 8,700 RPM I would get detonation, that is pre-ignition of the fuel and stop the engine. What that means is the fuel mixture would ignite when the piston was on the way up, and that results in a sudden stoppage.

This engine has a fuel pump, it is part of the cam shaft. The cam acts as a pump when it turns. So it has a fuel regulator on it. The excess fuel is returned to the tank and the remainder goes to the carburettor. The engine also uses the down stroke of the piston to compress the fuel/air mixture and send it to the intake manifold. So it is a poor man's super charger, force feeding the fuel air/mixture to the engine.

I determined the regulator was not working correctly. It has a tiny diaphragm in it. All the YS engine gurus said that the diaphragm was not working correctly, replace it. I got the part (actually a couple of them), and went about trying to figure out how to get into the regulator to change it. It took several emails and a couple Radio Control forums to learn that the "s" model regulator simply pries apart and snaps back together again. That took about six weeks of research.

Got the diaphragm replaced and went to the field. No joy, finally I figured out I had the check valve in backwards. The check valve is in the return line to the fuel tank and keeps the pressure up in the tank and keeps the fuel from flowing backwards. With the check valve in backwards, no fuel was getting to the pump!

Got that straightened out, and fire that sucker up. Man it ran rich but fast and powerful. I did not TACH the engine, since it was new rich was good thing for the engine to break in on. But it sure and hell was turning a lot faster than 8,700 RPM, no detonation, no sudden stoppage.

So I flew it. The cheapo airplane could not settle down, it was sensitive as hell. After about 6 minutes I ended up auguring the bird. Destroyed the fuselage, buried the engine two inches in the ground and damaged the wing. But now I know the engine is good to go. Man-o-man, that engine is some powerhouse!

I washed off the dirt, cleaned out the fins (had some balsa stuck in there) and checked over the engine. It is fine. No damage except to my ego.

Now I need another plane!