Tried the YS 140 sport (very nice engine BTW) in an extreme flight yak 74". Not nearly enough power for ANYTHING and really thirsty on very expensive fuel. Went to the OS 160 and Slimline muffler and never looked back. Run it with a Perry pump and put the tank on the CG. Use a 2 oz header tank and you'll never have a hickup or dead stick ! Balance the plane with the header tank full. I use a XOAR 18 x 8 . Found the 18x6 would let the engine wind up a little too much.

You need to spend some time tuning and breaking in. Set the low needle to 1 turn out from where it will fall into the carb case and then adjust the pump and high speed. This engine just keeps getting better and better with a really cool sound.

Open throttle and choke 5 spins (make sure fuel is drawing into the carb first), then flip backwards with a gentle flip and it will start everytime! Your buddies jaws will drop Did I mention that for glow fuel the 10% Omega is CHEAP!

Good Luck - hope you go OS (and they're cheap too!!)