YS120AC problems

[Dean Pappas]

Hello Bruce and Peter,
As you know, the regulator screw is both the idle and mid-range adjustment. A tight (non worn-out) AC will idle beautifully with a rich regulator. If it is only a little bit rich, then the engine will appear to subtly richen at 1/2 throttle and full power in the air. You may not even notice much of a rich transition, but this does happen. If the regulator is set even more rich, then the idle-to-WOT transition will be slow and blubbering rich.
 
What we need to know to help you better is whether the engine is definitely rich during this slow transition. You can prove this by briefly pinching the fuel feed line  as you push the throttle up. Stay out of the prop's way as you do this, as it may backfire lean and spit the prop off! If the pinch test improves the transition, then lean the regulator 1/8 turn at a time, and reset the needle valve at full throttle, each time. I have seen the regulator screw run anywhere between one turn out from flush and several turns in from flush with the housing. Put a fresh O.S. F type plug in the motor, as well. 
 
When you say that it smokes a lot, does that mean while running (probably rich) or after the engine stops (probably lean)?
 
Let us know how it goes,
    Dean Pappas

 

Hi Peter,

 

I am still having problems getting my YS120AC to run properly, even after putting in a new piston and ring.

The engine seems to idle okay, but is sluggish to pick up revs, even after adjusting the needle. I have replaced the regulator plunger and ring and fuel line, but no improvement. It also smokes a lot in my opinion. Have you got any ideas! 

 

Regards,

Bruce Hunter

jhbh at tpg.com.au

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