O.S. Engines Pre-2000 Pumped Engine Carbs - Manual

HOW TO PROPERLY SET YOUR O.S. PUMPER ENGINE’S CARBURETOR
These instructions describe the proper procedures for adjusting the carburetor of the following O.S. pumped engines:
O.S.- .46SF-P
O.S.- .46SF ABC-P
O.S.- .61SF-P
O.S.- .61SF ABC-P
O.S.- .61RF ABC-P
O.S.- FS-120 Surpass w/pump
The O.S. .61 RF ABC Hanno and FS-120 Surpass SP (supercharged) have their own special instructions.
These are all high-performance, top-of-the-line engines. They are all designed to give maximum performance.
Because of this, O.S. recommends that you use only a premium 2-stroke fuel with 10% or 15% Nitro. The fuel must
contain high-quality lubrication or your engine may become damaged. 2-stroke fuel must be used in all of the
engines listed above, even the FS-120 Surpass. Your O.S. pumper engine must have its carburetor correctly set if
you are to get the proper performance form the engine. If the carb is incorrectly set, you will have difficulty
achieving a good transition and reliable idle.
First, make sure the engine has the correct propeller. An incorrect propeller will cause the engine’s full-throttle
RPM to be too high or too low. The goal is to get the full-throttle RPM within a specific range. Any propeller that
will give you that RPM on the ground, and give you proper flight performance is correct. The actual diameter and
pitch is irrelevant if the engine is being run correctly. Listed below are the RPM ranges to use, and the props we use
to bench-test the engines. The bench-test props are also good props to use as a starting point in finding the best
flight prop.
Bench Test
Engine RPM Range Propeller
.46 SF-P mid 11,000's 11x7, 11x8
.46 SF ABC-P mid 11,000's 11x7, 11x8
.61 SF-P mid 11,000's 12x7, 12x8
.61 SF ABC-P mid 11,000's 12x7, 12x8
.61 RF ABC-P mid 11,000's 12x7, 12x8
FS-120 Surpass mid 9,000's 15x8
To start the engine when the carb is not set, gently close the high-speed needle all the way. Open it about 1 to 1-1/4
turns. Choke the engine as necessary, and then start it at around ½ throttle or below. Allow it to warm up about 30
seconds, then smoothly advance the throttle to full speed.
Once the engine is at full throttle, you can begin to lean the high-speed mixture. Use a tachometer as you make this
adjustment. If you do not use a tach, you will have difficulty finding the correct setting.
At full throttle, lean the engine carefully and slowly. As the RPM increases, there will be a bit of lag between the
time you adjust the needle and the response of the engine. Allow 10 to 15 seconds for the RPM to stabilize. Lean
until you see no increase in RPM. At this point, lean the engine ONE click at a time, with a pause to allow the RPM
to stabilize. Continue, one click at a time, until you see the first drop in RPM, then richen one click. Your engine
should now be at the maximum RPM setting you had before the RPM dropped. This is the correct high-speed
needle setting.
Now, drop the engine to ½ throttle, then bring it back up to full. It should reach the same top RPM.
If your engine has not been run much, it may not accept being leaned. If the engine will not come up to the proper
RPM range as it is leaned, but instead sags in RPM rather quickly as it is leaned, the engine may need more break-in
time. Your engine should be broken-in according to O.S.’s instructions.