Sierra Timer Base 18-99423 for Johnson Evinrude 6 Cylinder Cross Flow Engines 1979-1988

The Sierra 18-99423 Timer Base is an ignition component designed for Johnson/Evinrude 6 cylinder Cross Flow outboard engines equipped with twin power packs. The timer base works with the ignition system to regulate spark timing across the engine's cylinders, and is a common wear-and-replace item when an outboard develops rough running, misfires, or inconsistent timing at various RPM ranges. Replacing a worn or failing timer base restores accurate ignition timing and helps the engine return to smooth, reliable operation.

This timer base is built to fit the Johnson/Evinrude 6 cylinder Cross Flow engine family covering the 1979-1988 model years, across the 150, 155, 175, 185, 200, and 235 HP outboard variants that use twin power packs. It is intended as a direct fit for these applications and is cross-referenced to several factory OEM part numbers, making it easy to identify as the correct replacement when servicing these engines.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-99423
• Product Type: Timer Base
• Compatible Engine Family: Johnson/Evinrude 6 Cylinder Cross Flow
• Compatible Horsepower: 150, 155, 175, 185, 200, 235 HP
• Compatible Model Years: 1979-1988
• Power Pack Configuration: Twin power pack
• Weight: 0.8 pounds
• Product Dimensions: 7 x 5 x 3 inches
• UPC: 808282394547

Fitment

• Johnson/Evinrude 6 cylinder Cross Flow engines with twin power packs: 150, 155, 175, 185, 200, and 235 HP, 1979-1988

Replaces (OEM)

• 763783
• 583376
• 582041
• 581812
• 583127
• 583128

Frequently Asked Questions

What engines does the Sierra 18-99423 timer base fit? It fits Johnson/Evinrude 6 cylinder Cross Flow outboard engines with twin power packs, covering the 150, 155, 175, 185, 200, and 235 HP models from 1979-1988.

Does part 18-99423 work with single power pack ignition systems? No, the Sierra 18-99423 timer base is designed for the twin power pack configuration used on 1979-1988 Johnson/Evinrude 6 cylinder Cross Flow engines, not single power pack setups.

What OEM part numbers does 18-99423 replace? This timer base cross-references to OEM numbers 763783, 583376, 582041, 581812, 583127, and 583128.

How much does the timer base weigh? The Sierra 18-99423 timer base weighs 0.8 pounds.

What are the dimensions of this timer base? It measures 7 x 5 x 3 inches.

What symptoms indicate a timer base needs to be replaced? Rough running, misfires, or inconsistent ignition timing across RPM ranges on a Johnson/Evinrude 6 cylinder Cross Flow engine are common signs that the timer base, such as Sierra 18-99423, needs replacement.

Is the Sierra 18-99423 a genuine Sierra part? Yes, 18-99423 is a Sierra-brand ignition timer base, sold under Sierra's own part number.

Will this timer base fit engines outside the 1979-1988 range? The Sierra 18-99423 is specified for the 1979-1988 Johnson/Evinrude 6 cylinder Cross Flow engine range with twin power packs; fitment outside those years is not confirmed.

Does the timer base come with mounting hardware? The listing covers the Sierra 18-99423 timer base component itself; no additional included hardware is specified.

Can I use the UPC to verify I'm ordering the correct timer base? Yes, the Sierra 18-99423 timer base carries UPC 808282394547, which can be used to confirm the correct product when ordering.

What horsepower ratings use this timer base? The 150, 155, 175, 185, 200, and 235 HP Johnson/Evinrude 6 cylinder Cross Flow engines with twin power packs use the 18-99423 timer base.