YS are the best four stroke engines on the market. The people that have problems, simply don't take the time to learn how to tune and run them correctly. I ran a DZ160 flying pattern for 10 years and 100's of flights. In that time i had 2 dead sticks. One was the plug failed and the other was from a piece of silicon fuel tube blocking the needle valve.
The only maintenance was to adjust the tappets and occasionally to replace O rings.
I've had 13 of which i still have 11, ranging from the FZ63 to the DZ175cdi in my current pattern ships. I also have 2 x DZ185cdi's on order and am waiting for the DZ70cdi to be released.
YS's love nitro, especially the DZ range which are a high performance engine. Never run them lean as that is the reason they throw props.
People complain about the price, but if you want performance you can't go past them. Saitos and Magnums etc. are just your every day run of the mill engines that give average performance.
GO YS!!