I have just finished a gas/ignition conversion on my OS 91FS surpass. It is using muffler pressure with the stock carb and 20:1 oil. The ignition is a Rcxcel with thier 1/4-32 plug. It runs great. Starts easily without any kickback (handstart).

The carb needles were pretty sensitive. After some time and fine adjustments, it starts, idles and runs to full song nicely. However, It does have some intermitant stumbles and midrange hickups.. But when cycleing the throttle from idle to ful in succession 2 or 3 times it smoothes out.

I have a Perry pump and Oscilating pump on the way from Tower. I also have a Ironbay regulator and a couple Cline regulators to play with.

I am mentioning my OS91FS only because I am also planning on converting my Saito 150. The Saito is currently in a 25% scale Cub. What I am learning from the OS91FS I will apply to the Saito.