There are two different products being discussed here. Fuel stabilizer, sold by Sta-Bil, STIHL, Briggs & Stratton, and I am sure by others, is added to fuel to prevent oxidization and prolong shelf life. I use it in every 5 gallon can I bring home, and mix my two-stroke out of that, and my carb goo problems are gone. I pulled my TORO Suzuki two-stroke out of the shed the other day, and it had been sitting for 6 months, started right up. I used to have to de-slime the carb if it sat for a month, since the bowl has a huge atmospheric vent.
The de-carbonizer STIHL is marketing is mainly for the four-stroke blower and trimmer that uses a pre-mix. In some areas of the country, not all, these engines are getting carbon deposits on the ex valve, and when a leak down test shows anything over 10%, the engine will lose performance. The EDTA de-carbonizing liquid can be poured through the spark plug hole, with both valves open on overlap with the piston at TDC. Let it sit overnight and flush it out, run the motor, then do the leak down test again. I have seen it take a motor with 20% down to 5% with one treatment. Best use is probably to just do it twice a year if carbon buildup is a problem. The new Ultra full synthetic oil has shown to do a good job of keeping carbon problems away.
It would work on a two-stroke, but since there are no metel to metal sealing, like valves and seats, carbon problems don't cause as much trouble.
