Sierra 18-99391 Timer Base for Johnson Evinrude 6 Cylinder Outboards, 185-250 HP 1988-2001, Replaces 584586 583533 763775

The Sierra 18-99391 timer base is a replacement ignition timing component for Johnson and Evinrude 6 cylinder loop charged outboard engines equipped with Quick Start and S.L.O.W. Systems. The timer base controls ignition timing advance as the throttle is opened, working in conjunction with the engine's ignition system to deliver correct spark timing across the RPM range. It uses a mechanical lift design to translate throttle linkage movement into timing advance.

This timer base is built for 6 cylinder Johnson/Evinrude outboards rated 185, 200, 225, and 250 HP from 1988 through 2001 that use the loop charged, Quick Start, and S.L.O.W.-equipped ignition setup. It is a direct-fit replacement for the OEM timer base assembly and is intended to restore correct ignition timing operation on engines with a worn, cracked, or malfunctioning original unit. Installing a new timer base can resolve hard starting, rough idle, misfiring, or inconsistent timing advance caused by a failing original component.

The unit ships as a complete timer base assembly ready to install in place of the original equipment part, using the OEM mounting points and linkage connections. It weighs 0.9 pounds.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-99391
• Product Type: Ignition Timer Base
• Compatible Engine Configuration: 6 Cylinder, Loop Charged, Quick Start and S.L.O.W.
• Compatible Horsepower: 185, 200, 225, 250 HP
• Compatible Years: 1988-2001
• Lift Type: Mechanical
• Weight: 0.9 pounds
• Product Dimensions: 8 x 5 x 3 inches
• UPC: 808282394240

Fitment

• Johnson/Evinrude 6 cylinder loop charged engines with Quick Start and S.L.O.W., 185, 200, 225 and 250 HP, 1988-2001

Replaces (OEM)

• 584586
• 583533
• 763775

Frequently Asked Questions

What engines does the Sierra 18-99391 timer base fit? It fits Johnson/Evinrude 6 cylinder loop charged outboard engines with Quick Start and S.L.O.W. Rated at 185, 200, 225, and 250 HP, built between 1988 and 2001.

What OEM part numbers does this timer base replace? The Sierra 18-99391 timer base replaces OEM numbers 584586, 583533, and 763775.

How much does the 18-99391 timer base weigh? It weighs 0.9 pounds.

What are the dimensions of the timer base? The Sierra 18-99391 timer base measures 8 x 5 x 3 inches.

Is the timer base a mechanical or electronic unit? It uses a mechanical lift design to advance ignition timing as the throttle is opened.

Does this timer base work with S.L.O.W.-equipped engines? Yes, the 18-99391 is designed for 6 cylinder Johnson/Evinrude engines equipped with both Quick Start and S.L.O.W. Systems.

Will this fit a 200 HP Evinrude from 1995? Yes, provided it is a 6 cylinder loop charged model with Quick Start and S.L.O.W., the 18-99391 timer base covers 185-250 HP engines built 1988-2001, which includes that engine.

What symptoms indicate the timer base needs replacement? Hard starting, rough idle, misfiring, or inconsistent ignition timing advance on a covered Johnson/Evinrude 6 cylinder engine can indicate a worn or failing timer base like the 18-99391 needs replacement.

Can I cross-reference this part using my old OEM number? Yes, if your old timer base is stamped 584586, 583533, or 763775, the Sierra 18-99391 is the correct replacement.

Does installing the 18-99391 require any modification to the engine? No, it is a direct-fit replacement that installs at the OEM mounting points and linkage connections without modification.

Is this the complete timer base assembly? Yes, the Sierra 18-99391 ships as a complete, ready-to-install timer base assembly.