How do I install a Richard Sohn metering pump adapter on a Mazda RX-7 FB?

Installing a Richard Sohn metering pump (OMP) adapter on a 12A or 13B FB RX-7 is a Moderate difficulty project. It requires some basic custom fabrication for the reservoir bracket and some simple wiring.

The adapter acts as a blocking plate and shaft pass-through that sits between the engine's front cover and the stock OMP. This allows the stock pump to draw clean 2-stroke oil from an external reservoir instead of dirty engine oil from the sump, while keeping the factory mechanical throttle linkage intact ⁴.

Parts You'll Need:

• Richard Sohn Adapter: You typically have to contact him directly to order, especially for the 12A variant ².
• Two OMP Gaskets: One goes between the engine and the adapter, and the second goes between the adapter and the OMP ⁴.
• 2-Stroke Oil Reservoir: A popular choice is a Yamaha Razz/Riva oil tank. The plastic won't degrade from 2-stroke oil, it's sized well for the engine bay, and it has an integrated fluid level sensor ².
• Clear Polyurethane Hose: This material is oil-resistant and lets you visually inspect the line for air bubbles ².
• OMP Rebuild Kit (Highly Recommended): Using a kit with Viton O-rings (like those from Lowe Performance) while the pump is off will significantly extend its lifespan ⁴.

Installation Procedure:

1. Remove the Stock OMP: Disconnect the oil feed lines to the carburetor and pop off the mechanical linkage rod that connects to the carb's throttle arm. Unbolt the OMP from the front cover.
2. Rebuild the OMP: Since you have the pump off the car, tear it down and replace the old O-rings with Viton replacements to prevent future leaks.
3. Install the Adapter: Place your first new gasket against the engine's front cover, position the Sohn adapter, place the second gasket on the adapter, and bolt the stock OMP over it. I don't have a verified torque figure for the OMP mounting bolts on this specific engine, so don't take a number from me on it—check your factory service manual. The standard procedure is to clean all mating surfaces thoroughly and tighten the bolts evenly in a criss-cross pattern to avoid warping the pump housing.
4. Reconnect the Linkage: Reattach the mechanical linkage rod between the OMP lever and the carburetor throttle arm. This linkage is critical because it modulates the oil delivery based on your throttle position ⁶.
5. Mount the Reservoir: Fabricate a bracket out of sheet aluminum to securely mount your 2-stroke oil tank in the engine bay ².
6. Plumb the System: Connect the clear polyurethane hose from the reservoir to the feed inlet on the Sohn adapter.
7. Wire the Warning Sensor: If you use the Yamaha tank, wire its level sensor in parallel with the RX-7's stock oil level light and warning buzzer. This ensures that if either the engine oil sump or the new 2-stroke reservoir runs dry, your dash warning will trigger ².

Once everything is bled and running, it's good practice to slap a custom "2-stroke oil" label on the new reservoir cap so nobody accidentally fills it with standard engine oil in the future.