Oil Injection Block Off, System Removal - Mercury 2.0, 2.4, 2.5 Liters
- Mike Hill
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- Jun 16, 2024
- 5 min read
The Buckshot Racing #77 Mercury V6 Oil Injection Block-Off Kit is designed for Mercury 2.0 Liter, 2.4 Liter, and 2.5 Liter two-stroke V6 outboards being converted from factory oil injection to premixed fuel.
This kit is commonly used by racers, engine builders, tuners, and performance boat owners who want to eliminate the original mechanical oil injection pump system and run a controlled fuel-and-oil premix.
Many high-performance Mercury V6 owners choose premix when building modified, high-RPM, or race-use engines because premix removes the dependency on aging oil injection parts, oil hoses, pump drive components, warning modules, check valves, and remote oil tank hardware.
This is especially common on performance Mercury 2.4L and 2.5L engines that see elevated RPM, aggressive acceleration, surfacing propeller use, or race-duty operation.
This oil injection block-off kit is compatible with Mercury-style applications using part numbers 818304A1, 8M0095447, 43453, 43453T, and 32509. It is intended for Mercury V6 two-stroke outboards where the oil injection pump is being removed and the engine will be operated on properly mixed premix fuel.
What the Oil Injection Block-Off Kit Does
The factory Mercury oil injection system uses a crankcase-driven oil pump to meter oil into the fuel system. When converting to premix, the oil pump is removed and the opening in the crankcase must be sealed properly.
The Buckshot Racing #77 block-off kit replaces the removed oil pump assembly with a block-off plug, O-ring, and mounting hardware to seal the oil pump cavity.
A proper block-off installation prevents crankcase air leaks, oil seepage, and contamination while allowing the engine to operate on premixed fuel. Because two-stroke engines rely on oil in the fuel for internal lubrication, the engine must never be run on straight gasoline after the oil injection system is removed.
Why Racers and Builders Convert to Premix
Premix is popular in Mercury performance builds because it gives the owner direct control over the fuel-to-oil ratio. Instead of relying on an older mechanical oiling system, the operator mixes the correct amount of two-stroke oil directly into the fuel tank before running the engine. This simplifies the engine, removes several potential failure points, and makes the fuel system easier to inspect and service.
The tradeoff is responsibility. Once the oil injection system is removed, every gallon of fuel must be mixed correctly. If the boat is filled with straight gas by mistake, the engine can suffer rapid bearing, piston, ring, and cylinder damage.
Installation Overview
Begin by disconnecting the battery and making sure the engine is cool. Work in a clean, well-ventilated area and keep dirt out of the intake, crankcase, fuel system, and oil passages.
Drain or remove oil from the remote tank, engine-mounted oil tank, oil hoses, and pump area to prevent spills.
Remove the cowling and any components blocking access to the oil injection pump.
Carefully disconnect the oil lines from the pump and cap or remove unused lines so they cannot leak, drip, or allow contamination into the engine area.
Unbolt the oil pump from the crankcase and remove the pump, O-ring, long drive shaft, sleeve, and related oil injection hardware as required for your specific Mercury V6 configuration.
Clean the oil pump mounting surface thoroughly. The sealing area must be free from old gasket material, oil residue, corrosion, and debris.
Install the Buckshot Racing #77 block-off plug with the supplied O-ring and mounting screws.
Use only a light film of appropriate marine sealant if needed around the o-ring sealing area.
Do not overuse sealant, and do not allow sealant to enter the crankcase.
Tighten the supplied screws evenly and carefully.
The block-off cap should be secure, but over-tightening can damage the cap, threads, or sealing surface.
Reinstall any removed components and inspect the area for proper clearance, clean routing, and secure hardware.
Premix Fuel Requirements
After installation, drain any unmixed fuel or clearly confirm the fuel in the tank is properly mixed before starting the engine.
The correct fuel-to-oil ratio depends on the engine build, oil type, break-in status, operating RPM, and Mercury or engine builder recommendation.
Many Mercury V6 premix applications use ratios in the 24:1 to 50:1 range depending on use. Fresh rebuilds, race engines, and break-in procedures may require a richer oil mixture than normal recreational use.
Always mix fuel and oil thoroughly before running the engine. Use high-quality marine two-stroke oil appropriate for your Mercury V6 outboard and never assume the tank is mixed unless you personally verified it.
Warning System and Alarm Notes
Removing the oil injection system changes the warning system. The factory oil warning circuit and oil injection alarm will no longer function as originally designed once the oil injection pump and related components are removed.
However, the over-temperature alarm should remain functional.
On many Mercury V6 warning systems, the overheat alarm circuit uses the tan/blue wire. With the key on, grounding the tan/blue temperature warning lead should activate the warning horn.
This test helps confirm that the over-temperature alarm circuit still works after the oil injection conversion. If you are unsure how your warning system is wired, consult the correct Mercury service manual or have the system checked by a qualified marine technician.
The oil injection warning module may be removed or disconnected during conversion, depending on the engine setup. Any unused wiring should be insulated, secured, and protected from short circuits. Do not remove or disable the over-temperature warning circuit.
Crankshaft Gear and Internal Volume Note
On Mercury V6 oil injection conversions, many builders leave the crankshaft oil pump drive gear in place unless the engine is being fully disassembled and properly reconfigured.
Removing internal components without understanding the crankcase volume and airflow effects can change how that cylinder behaves. If the powerhead is apart and the gear is being removed, the work should be handled by an experienced Mercury V6 builder.
Label the Boat Clearly
After converting to premix, label the boat clearly so no one accidentally adds straight gasoline. Place visible “PREMIX ONLY” labels near the fuel fill, fuel tank, dash, and engine rigging area. This is one of the most important steps in the conversion because one fueling mistake can destroy a two-stroke powerhead.
Final Startup and Inspection
Before starting the engine, verify that the block-off plug is sealed, all unused oil hoses are removed or capped, all wiring is secured, the battery is reconnected, and the fuel tank contains the correct premix.
Start the engine on a proper water supply and let it idle briefly while inspecting the block-off area for leaks or air intrusion. Confirm stable idle, normal water flow, and proper warning horn function before running the boat.
After the first run, remove the cowling and inspect the block-off plug, fasteners, fuel system, and wiring again. On performance engines, continue monitoring plug color, piston wash, temperature, water pressure, and fuel quality as part of normal tuning.
Buckshot Racing #77 Note:
The Buckshot Racing #77 Mercury V6 Oil Injection Block-Off Kit is a practical upgrade for Mercury 2.0L, 2.4L, and 2.5L two-stroke outboards being converted to premix fuel.
Compatible with Mercury-style part numbers 818304A1, 8M0095447, 43453, 43453T, and 32509, this kit gives racers, builders, and performance boat owners a clean way to remove the factory oil injection pump and seal the crankcase properly.
For Mercury V6 race engines, lake motors, drag boats, tunnel hulls, and high-performance outboard builds, a properly installed oil injection block-off kit helps simplify the engine, improve serviceability, and support reliable premix operation when fuel is mixed correctly every time.
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