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Mercury FourStroke 2.5 - Carburetor Adjustments; Idle Speed; Pilot (Idle Mixture) Screw

Mercury FourStroke 2.5
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Carburetor and Fuel Pump
Page 3A-8 90-8M0065421 NOVEMBER 2012
Carburetor Adjustments
Pilot (Idle Mixture) Screw
IMPORTANT: The pilot mixture screw is set at the factory to allow the engine to meet established government emission
specifications. The pilot mixture screw is normally hidden with a tamperproof plug. However, if the carburetor requires
rebuilding and/or cleaning, the plug can be removed and the pilot mixture screw removed to facilitate cleaning. Follow the
procedure below when the carburetor is rebuilt or cleaned.
1. When removing: Record the number of revolutions to lightly seat the pilot mixture screw.
2. When installing: Turn the pilot mixture screw in (clockwise) until lightly seated. Then back the screw out the same number
of turns as measured during removal.
3. After installation, install a new tamperproof plug.
a - Pilot mixture screw (tamperproof plug removed)
Idle Speed
After the pilot (idle mixture) screw has been properly installed, adjust the idle speed screw to specification.
Tightening the screw increases the engine speed.
Loosening the screw reduces the engine speed.
Engine RPM (2.5/3.5)
Idle speed (neutral) 1400 ± 50 RPM
Idle speed (forward) 1300 ± 50 RPM
a - Idle speed screw
a
26506
a
26509

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