I came on line this evening after a nice day at the field with the EXACT setup you are using (YS1.20NC and WM Fun World 3D). What you describe is my condition.

I have two YS 1.20 NCs. The first one, purchased about 6 years ago is from the outside identical to the one that is now installed in the World Models plane. The one installed in the WM is about 2 years newer than the first one.

THe first engine runs like a clock. Contrary to one of the posts, your expectation should be that the YS will purrr. Transitions should be immediate and completely smooth, idle should be stable even when very, very slow (so you almost hear the valves ticking away), and you should be above 9K RPMs turning a 16 x 8 APC (what YS performance recommends and seems to optimize the power curve on this engine). Like one of the other posts, I also used to run a 15 x 8 but the thrust is more with 6 x 8 when doing the back-of-the-napkin calculus (raw feel).

Anyway, the reason for the engine history is that the second YS never ran well...from the start. I had sent this to YS performance (after being so happy with my first one) and they drilled it out as the recommended cure. Apparently there were a bad batch of engines out there that would never lean or richen (I can't remember now which way it was).

After the drilling (side counted at the time) it did run better but still nothing like the first engine. Now that it is mounted inverted, it does exactly what yours is doing (vibration, etc). I have a little rpm drop off when the ignitor is disconnected but no severe. My main problem is the transition. If I goose it it really stumbles.

We tinkered with the high and low (I never even thought of touching the low on my first engine) and honestly, I couldn't tell when it was running better or worse.

I was actually hoping to come on line to find the direction I should be turning the low end as I probably have it all messed up now.

I will stay tuned and let you all know if I find something out.

Trevor Dearman