Not the best video but it gives you an idea of how it flies with a saito 180 four stroke on the Yak.
http://www.youtube.com/watch?v=MJhGPG7pVPc
Sorry to hear the gasser did'nt work for you. This is a typical 11-12 pound plane, if it were 9lbs it would be very light. With the saito 180 in it it is not too heavy and it has plenty of power. The new Saito 180 did shake it bad until I got it broke in and now it is great. There is no sense (maybe $) in going with the Saito 150, it is the same weight and less power.