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FS-120 Surpass II HS won't adjust

Old 07-01-2007, 08:12 PM
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Default FS-120 Surpass II HS won't adjust

I have a FS-120 Surpass II pumped which I inherited. The motor was run previously and I have
tried running this engine on the test stand with a 15 x 8 APC prop.
When going to full throttle from any position between idle and 3/4 it loads up and dies.
The HS needle doesn't appear to have any effect when adjusted in either direction.

The owners instructions which were provided by O.S. via email don't give details for parts
of the carburetor or mention any other adjustment other than HS needle. There is also
conflicting info between page 5 and page 6 regarding initial needle valve setting.
Is there a parts drawing and associated part number list for this engine which will
detail the carburetor model?

Thanks
Old 07-02-2007, 10:14 AM
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Default RE: FS-120 Surpass II HS won't adjust

For pumped engines, here's how you set them:

Your O.S. Max engine with pump should be set up in a slightly different manner than a non-pumped engine. Most modelers tend to get them set with the mixture too rich.

One sign your engine's not adjusted correctly would be surging at full throttle. This almost always means it's too rich. Also, the idle may be too rich no matter what you do to the idle mixture. If the idle is leaned a lot, but it's still too rich, the high-speed needle's too rich and needs to be properly set.

To get a good setting, you need to use a tachometer. Once the engine's had enough running to accept being leaned to peak RPM, use the tachometer to lean the engine to its peak.

At full throttle, lean the engine until the RPM stops increasing. Continue to lean the engine to the first sign of RPM drop or detonation. When you get to that point, richen to the point just before you had the RPM drop or detonation and leave the needle there. DO NOT lean to peak and then richen your usual 1/4-1/2 turn.

With a good-quality fuel, the pump system will insure that the engine receives enough fuel. The regulator in the system will make sure that the mixture stays correct as you change the throttle positions. Fly the engine to see how the mixture may change as the engine unloads in the air. You may have to lean or richen slightly, depending upon how it acts. Once you've found the proper setting, you should note the change from the absolute maximum lean position. Now you have a repeatable setting for your engine.

Newer O.S. engines with pumps have a broader range for the needle setting, but you can use the same method for all of them.

If this doesn't work, and your high-speed needle is less than 3/4 turn out when leaned to just rich of peak RPM, then you may have a bad needle seat. That will require a new carburetor body, which is no longer available from O.S. You'll have to get the part through a swap shop, auction site, or dealer who sells to collectors.
Old 07-03-2007, 06:49 PM
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Default RE: FS-120 Surpass II HS won't adjust

Thank you for the information. Is this carburetor the C-13 model?
What screw on the carb adjusts the idle and which direction is used to lean
the setting?
Is it possible to find a parts break down for this model?
Old 07-05-2007, 01:06 PM
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Default RE: FS-120 Surpass II HS won't adjust

If you send an email to our address below, we can send you the instruction manual for the engine.
Old 07-05-2007, 04:59 PM
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Default RE: FS-120 Surpass II HS won't adjust

Will the instructions include a parts breakout and idle adjust info?
Old 07-06-2007, 10:23 AM
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Default RE: FS-120 Surpass II HS won't adjust

Yes.

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