As Mercury two-stroke outboards continue to age, many owners choose to remove the factory AutoBlend oil injection system and convert to a premixed fuel and oil mixture.
This is a popular upgrade for fishing boats, bass boats, performance boats, and race boats because it eliminates aging oil pumps, warning modules, hoses, check valves, and drive components that can become unreliable after decades of service.
Buckshot Racing #77 offers Oil Injection Block-Off Kits (8129962) that safely replace the factory oil pump while properly sealing the oil pump mounting location. The kits are available in two options to match your budget and application:
- Option 1 (Standard): Durable black thermoplastic block-off kit for dependable everyday service.
- Option 2 (Premium): Black billet aluminum block-off kit, CNC-machined from aircraft-grade aluminum for maximum durability, improved appearance, and long-term corrosion resistance.
Both versions install using the factory mounting holes and provide a clean, professional solution when converting your engine to premix.
Why Remove the Oil Injection System?
Mercury's oil injection system was an excellent convenience feature when new, automatically delivering the correct amount of two-stroke oil based on engine speed. However, many of these systems are now 25 to 40 years old. Over time, oil pumps, drive gears, hoses, sensors, and check valves can deteriorate or fail.
Because the oil injection system is solely responsible for engine lubrication, a failure can quickly result in piston damage, bearing failure, or complete powerhead destruction.
For this reason, many experienced Mercury technicians and performance boaters choose to remove the oil injection system during a rebuild and operate the engine on premixed fuel and oil.
Properly Seals the Crankcase
After removing the factory oil pump, the opening in the crankcase must be sealed correctly. An improperly sealed pump cavity can create crankcase air leaks that affect idle quality, fuel delivery, and engine performance.
The Buckshot Racing #77 Oil Injection Block-Off Kit completely seals the oil pump mounting location while protecting the internal drive gear cavity and maintaining proper crankcase pressure. The result is a reliable, leak-free conversion that allows the engine to operate safely on premixed fuel.
Most Important!
The mounting holes measure approximately 1-7/8 inches center-to-center, allowing the kit to install using the factory hardware. While there is no complete cross-reference for all these motors, we have not found one that did not fit with these measurements.
Fits Popular Mercury & Mariner Two-Stroke Outboards
These kits fit many Mercury and Mariner 2- cylinder, 3-cylinder, and 4-cylinder looper two-stroke outboards built from the mid-1980s through the mid-2000s, including engines with 3.375-inch and 3.500-inch cylinder bores.
Common applications include Mercury and Mariner 30HP, 30HP Jet, 40 HP, 45HP Jet, 50 HP, 55HP, 60 HP, 75 HP, 80 HP, 90 HP, 100 HP, 115 HP, and 125 HP carbureted two-stroke outboards widely used on bass boats, fishing boats, aluminum boats, utility boats, pontoon boats, and performance hulls.
Running Premix
Once the oil injection system has been removed, the engine must always operate on properly mixed gasoline and quality TC-W3 two-stroke oil. Many recreational boaters use a 40:1 premix ratio, while builders of modified, high-performance, and older outboards often prefer a 32:1 premix ratio.
Certain racing applications may require richer oil mixtures depending on engine modifications and operating conditions. Accurate fuel mixing becomes critical because the premix now supplies all engine lubrication.
Buckshot Racing #77 Tech Tip
If you're already rebuilding your powerhead or replacing crankshaft seals, bearings, pistons, or reeds, it's the ideal time to eliminate aging oil injection components. Installing a new block-off kit during the rebuild helps simplify the engine while removing one of the most common maintenance concerns found on older Mercury two-strokes.
The (1) black thermoplastic kit provides an economical, factory-style solution, while the (2) black billet aluminum version offers superior strength, premium appearance, and added durability for performance, offshore, and racing applications.
Final Thoughts
Thousands of Mercury and Mariner two-stroke outboards remain on the water because of their simplicity, reliability, and proven performance. Whether you own a 30HP, 75 HP, 80 HP, 90 HP, 100 HP, 115 HP, or 125 HP looper, the Buckshot Racing #77 Oil Injection Block-Off Kit provides a clean, dependable conversion from factory oil injection to premix operation.
Available in (1) black thermoplastic or an upgraded (2) CNC-machined black billet aluminum design, both kits are engineered to seal the crankcase properly and help keep these legendary Mercury two-stroke outboards running for years to come.
Contact Mike Hill at +1-714-697-1716 or email mike@buckshotracing77.com for technical support.