I just ran my ST 90 on Gasoline/Spark ignition for the first time today. The stock carb. works great with NO mods and it's turning a 14X6 MA K-Series prop 10,500 which is only 200 rpm's shy of what it turned on glow fuel. I am a bit confused why it didn't lose any more power. My little motor, the G51 lost about 500 rpm's and I expected about the same from the 90. This motor does not have the needle bearings in the rod and I have to run it at the same 16:1 ratio that I use in the G51. I have another one that I have put the needle bearings in the rod but still have some more work to do before it is ready to run. Also, i made an adapter to put a Walbro carb on it but decided to try the stock carb first and I am glad I did as it seems to run very good with it. I am running the timing at 28 deg. just like the G51. It idles very smooth and steady at 2000 rpm's with absolutely no hint of wanting to die and the transition is excellent even after prolonged idling.