The proprietary Saito gas carbs, sans the early FG-20 version, run spectacularly. I have three FG-21 and an FG14. One of the FG-21 has about 3 gallons run through and the oil comes out almost completely clear with no visible smoke except upon acceleration from a prolonged idle.

A good friend of mine has an FG-41TS with about 1 gallon run through. He says the exhaust oil is getting clearer each time he runs it. According to him the engine runs terrific but he is out of state so I'm taking his word on it.

John, my FG carbs do have a button with a spring in the middle of the carb. I assume this is for returning the pump diaphrams due to the lack of positive pulse pressure. It does not appear to seal anything. The pump diaphram has reed/flap valves like a Walbro. The FG-41TS carb appears to be same as used on the FG-21 albeit having a different part number. I searched for a carb rebuild kit for the 41TS to see if it used the same parts as a 21 but no luck finding one yet.