RE: Mid 90's OS FS120 Surpass Break In
To break in your old FS-120 Surpass, you want to use a fuel with 10%-15% nitro, either a fuel labelled for "2-stroke" or "4-stroke" engines. Open the high-speed needle about 1-1/2 turns if it's the pumped engine, and about 2-1/2 turns if it's a non-pumped engine. Open the throttle to full and choke the engine until fuel starts to "spit" out of the exhaust port. Un-choke the engine and briskly flip the engine several times to make sure it's clear. Apply the starter battery to the glow plug and apply the electric starter. If hand-flipping the engine to start it, flip it backwards against compression.
Once running, advance the throttle to full and run the engine as rich as possible without it quitting. You can leave the glow plug battery connected. Run the engine this way for at least 15-20 minutes. After that, you can lean the engine a bit at a time, progressing to peak RPM over the next 1/2-hour or so. If the engine will sustain running at a setting just rich of peak RPM, it's ready to fly.