If you are just starting out in pattern IMO forgett the YS its complicated enough to get through the sequence, you do not want to be messing about with an engine you don't know how to set up, also they need 20 - 30% nitro to run properly so any saving on fuel by going smaller in cubic capacity will be negated by the extra cost, the frustration of competition is enough you don't want to put yourself through more, just get an ordinary OS or similar to start with and fit the tank behind the firewall, when you notice the difference in trim during flight from the fuel being used up, that's when you will possibly be ready for the YS with its pump and the fuel tank back on the C of G, personnaly I use a Weston UK tuned Magnum with a Webra regulating valve to pump the fuel up too the engine and its less complicated than setting up the YS, which sits in a box unused.

This of course is my opinion only and will not correspond with anyone else I'm sure, ducking the flack, repel boarders Mr Christian. LOL

Mike