RCU Forums - YS 120F

James,

the instruction manual is basically the same as all the YS engines. The 120SF is the engine you have. This was essentially the first engine. Basically all the 120 parts will work...there are a few exceptions....namely the 120AC and the 120SC have a different crank and crankshaft ring...but parts like pistons, rings, sleeve and so on if the 120SF part is not available the 120FZ part will likely work.

http://www.centralhobbies.com/Engine...YS120SFEX.html

is the exploded parts view of you engine.

As for operation....the engine you have doesn't have the air bleed screw in the throttle barrel. So your idle adjustment is the regulator screw. In is lean CW and out CCW is rich.

It gets set the same way...as all the current engines. On the current engines the air bleed screw on the throttle barrel is a fine tuning adjustment and doesn't really have a huge affect. In the case of the older engines you set the regulator so that the low end is a good idle at about 2000rpm. Starting point for the regulator screw is flush. However if the engine has already been run I would start with the current setting. On these early engines it was much more likely the regulator screw to be moved off the "flush" with the case location than with the current engines. In todays engines the regulator is very rarely touched. But on these older engine is is often adjusted to get the idle mixture....

Since the engine is old and has some time on it and has sat dormant...I would recommend sending it to service. Its probably past due for bearings...and they will clean it all up and make sure its working. You don't always have to change the regulator diaphram...only is its deformed...Sitting for a long period of time its likely deformed...but Let the guys at Service take a look. They will fix it up for you and only change a part if its needed.

www.yspartsandservice.com

Your engine has not been in production for a long time. 1990 would be a good bet. Its almost time to hang antique plates on it. Chances are it has little run time on it...but who knows. Getting into it the Service guys will know what needs to be done and you won't be fighting it or just throwing parts at it in hopes it will work.

These machines make great power but they can get a little complex. Gaskets can dry out and leak, and O-rings can get old and hard. They are silicone and you would never run the same silicone fuel lines in a 17 year old fuel tank would would you?

I think you will be surprised at how little may need to be done...but a trained eye looking it over will give you a good shot and making it work properly.

I do most of my own engine work, and I sent a 120AC into service last fall. The reason was I didn't want to waste my time throwing parts at it. They tear it down and have all the parts sitting right there. If it needs it the engine gets it and is back together right away and running. I would have spent a couple weeks tearing it down and then looking at the parts ordering them and waiting to arrive. Then if I missed something it would not run properly and I would be waiting for a while longer for parts. So I just sent it to Richard and they fixed it up quickly and it runs like a top.

Troy Newman
Team YS Performance