Im building a Pica Waco bipe 1/5 scale.The box says the weight will be between 11-13 lbs maybe a little more.I want to use a four stroke engine and the specs. call for a 90 two stroke or 120 four stroke, I want more power then this and am considering the 140 DZ 0r the 140 sport.This engine will be cowled in and will need to use a muffler,A stock 4/s muffler will prob. work?My question which of these two engines will be the best,Power will prob. be at about 1/4 throt. most of the time and i will need a smooth transition from 1/4 -full throt. Idle should be excellent. I have never owned a YS engine,But i want one now, might use the engine for a Pattern plane later. Thanks for any help Randy Wallace