Based on what I read (and experienced 1 time), I think your problems will clear up with higher nitro. I keep hearing that ys loves 20% and higher nitro. I use 30% heli fuel. I do know one guy at my field who had erratic running problems with his ys (15% nitro). I gave him 1/2 gallon of my 30% and problems disappeared the first tank. He then tried using 15% again, problems returned. Now he only uses ys 20/20 fuel.

Guys at my field don't like ys engines. They say they are hard to tune. I believe it was because they never tried upping the nitro.

Do a search for ys in the glow engines forum. You will find a lot of info regarding ys and fuel.