YS 120 SF regulator problem
 

Hi Dave;

I have an old YS 120 SF (first ones) engine, it was running ok until now. At a given moment the engine (between flights) the engine did not start. I did everything imaginable to the tank, lines and hi needle with no results. I did have to check the regulator, seem to be clean.

The engine only starts at full throttle, and dies if lower than half throttle. The regulator is not working (apparently). The tank has good pressure even 1 minute after the engine dies.

Regulator is immaculately clean; the holes have been flushed with a syringe and some fuel line. The silicone parts are ok and the gasket seems ok (I know is a trouble some part) the knob on the regulator is toward the front.

Only problem I see is that the plunger once inserted into the regulator body.

Any thoughts?

Alexis

Sorry, my English is not good.

RE: YS 120 SF regulator problem
 

Sounds like you might have developed an air leak. Check all the o-rings and gaskets. At high speeds it isn't changing the air/fuel ratio enough to make the engine quit, but at lower RPMs the extra air is making the engine lean out and die.

David

RE: YS 120 SF regulator problem
 

Yes, there were some bubles in the fuel line.... more than normal.

Here are some photos of the regulator parts.

Te black neoprene part is a home made one.

Alexis

RE: YS 120 SF regulator problem
 

Dave:

Should the plunger have some movement once inserted into the regulator body and the spring and cap assembled.

I can see that they do not move. Even if the spring is almost not giving any pressure.

Where can i get this spare parts?

AT

RE: YS 120 SF regulator problem
 

Yes there should be movement of the plunger. If the plunger does not move the regulator does not work. Central Hobbies stocks parts for most YS engines. There are even exploded diagrams of the engines on their site if you need to know how it should go together.