I have several 4 strokes (Saito and YS). I think you should know also. A 4-strk YS engine does not have a pressure nipple on the exhaust tip nor does it have a crankcase pressure nipple on the bottome that removes excess oil. This motor uses crankcase pressure to basically Supercharge the fuel into the engine at higher than atmospheric pressure. A normal 4 strk puts 3-4 lbs of pressure into the tank through the pressure nipple, but a YS puts about 9 lbs of pressure into the tank. I wrap my fuel tanks in high strength packing tape with the string embedded in the tape to keep the tank from exploding. YS engines are a little different than your average 4-strk and cost more, but the performance aspect of the engine is second to none. The plumbing set up for a YS is a little different also as you have to use a one way valve for the pressure line and release tank pressure before you refuel or defuel. If this isn't done, the pressure will give you what is known as a YS bath as the tank will try to empty itself onto you from the 9lbs of pressure in there.

Example: my YS .91FZ is compariable to if not stronger than a Saito or OS 1.20 and my YS 1.10FZ is compariable to a Saito 1.50 in performance.

Here is a photo of my YS 1.10FZ with the plumbing. Looks like Frankenstien with all the tubing going everywhere, but there is some order to the caios.
http://derrick.myphotoalbum.com/view...album02&id=acv