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

Carburetor and Fuel Pump

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.

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)
Idle speed (forward)
a
Page 3A-8
a - Pilot mixture screw (tamperproof plug removed)
a
26506
a - Idle speed screw
26509
1400 ± 50 RPM
1300 ± 50 RPM
90-8M0065421 NOVEMBER 2012