Sierra 18-99178 Power Pack for Johnson/Evinrude 50 HP and 55 HP 2-Cylinder Engines (1971-1977)

The Sierra 18-99178 Power Pack is an electronic ignition module built to replace the original power pack on Johnson and Evinrude 2-cylinder outboard engines rated 50 HP and 55 HP from 1971-1977. The power pack controls ignition timing and spark delivery for the engine's 2-cylinder ignition system, and is a direct functional replacement for the original equipment module used on these outboards.

Constructed with a plastic housing to protect the internal electronics from the marine environment, the 18-99178 mounts using an engine mount configuration and is designed as a straightforward swap for the factory unit on compatible 90 cubic inch displacement gasoline 2-cylinder Johnson/Evinrude powerheads. It operates automatically once installed, requiring no manual adjustment during normal operation.

This power pack is intended for boat owners and marine technicians replacing a failed or aging ignition module on 1971-1977 Johnson/Evinrude 50 HP and 55 HP 2-cylinder outboards, restoring reliable starting and consistent ignition timing.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-99178
• Product Type: Power Pack
• Compatible Engine Brand: Johnson/Evinrude
• Cylinder Count: 2 Cylinder
• Horsepower Rating: 50 HP and 55 HP
• Model Years: 1971-1977
• Engine Displacement: 90 Cubic Inches
• Fuel Type: Gasoline
• Material: Plastic
• Color: Multicoloured
• Mounting Type: Engine Mount
• Weight: 0.7 pounds
• OEM Cross Reference: 581397, 764708, 18-5755

Fitment

• Johnson/Evinrude 2-cylinder engines, 50 HP and 55 HP, 1971-1977

Replaces (OEM)

• 581397
• 764708
• 18-5755

Frequently Asked Questions

What engines does the Sierra 18-99178 power pack fit? The Sierra 18-99178 fits Johnson/Evinrude 2-cylinder outboard engines rated 50 HP and 55 HP from 1971-1977.

What OEM part numbers does 18-99178 replace? This power pack replaces OEM numbers 581397, 764708, and 18-5755.

How much does the 18-99178 power pack weigh? The Sierra 18-99178 power pack weighs 0.7 pounds.

What material is the power pack housing made from? The housing is made of plastic, providing protection for the internal ignition electronics.

Does this power pack work with 3-cylinder or 4-cylinder Johnson/Evinrude engines? No. The Sierra 18-99178 is designed specifically for 2-cylinder Johnson/Evinrude engines rated 50 HP and 55 HP; it is not intended for engines with a different cylinder count.

How is the 18-99178 power pack mounted? It uses an engine mount configuration, matching the mounting setup of the original factory power pack it replaces.

Is the 18-99178 a direct replacement for the original power pack? Yes, the Sierra 18-99178 is built as a direct functional replacement for the factory power pack on compatible 1971-1977 Johnson/Evinrude 50 HP and 55 HP 2-cylinder engines.

What fuel type is this power pack designed for? The 18-99178 is designed for gasoline-fueled 2-cylinder Johnson/Evinrude outboard engines.

Does the power pack require manual adjustment after installation? No, once installed the 18-99178 operates automatically to control ignition timing without manual adjustment.

What is the engine displacement this power pack is designed for? It is designed for 90 cubic inch displacement Johnson/Evinrude 2-cylinder engines.

Can I use part number 18-5755 to cross-reference this power pack? Yes, 18-5755 is one of the OEM numbers the Sierra 18-99178 replaces, along with 581397 and 764708.