Fuel Pump Diaphragm Kit – Fits Mercury/Mariner 30-275 HP (Replaces 21-42990A10, 21-857005A1)

Product Details

This Fuel Pump Diaphragm Kit is designed for a wide range of Mercury and Mariner 2-stroke outboard engines from 30 to 275 HP, covering various models from the late 1960s through the early 2000s. It serves as a direct replacement component for engine-mounted fuel pumps, restoring proper fuel flow and pressure.

This component provides a direct interchange for Mercury part numbers 21-42990A10 and 21-857005A1, as well as aftermarket equivalents from Sierra (18-7817), GLM (40290), Quicksilver (857005A1), TaoYwMIK (21-42990A10), and SouthMarine (21-42990A10).

• Installs as a critical component in the engine-mounted fuel pump.
• Made from a durable black composite membrane designed for gasoline applications.
• Features integrated check valves to ensure correct, one-way fluid flow.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury/Mariner engines, it is critical to verify compatibility using your engine's serial number, as year ranges can overlap.

Technical Specs

Product Type

Fuel Pump Diaphragm Kit

Installation

Engine-mounted fuel pump replacement component

Fuel Type

Gasoline

Housing Material

Black plastic (composite membrane)

Housing Color

Black

Dimensions

6.0" L × 7.13" W × 0.5" H

Weight

0.02 kg (0.634 oz)

Other Technical Attributes

Check valves at bowl inlet and outlet ensure one-way fluid flow

What’s in the Box

• 1 x Fuel Pump Diaphragm Kit (21-42990A10/21-857005A1)

Installation Notes

1. Disconnect the negative battery cable and relieve fuel system pressure.
2. Place clean rags below the fuel pump to catch any spilled gasoline.
3. Carefully note the orientation of fuel lines, then disconnect them from the pump.
4. Remove the mounting bolts securing the pump to the engine block.
5. Disassemble the fuel pump housing to access the old diaphragm. Pay attention to the order of components.
6. Remove the old diaphragm and any associated gaskets. Clean the housing surfaces.
7. Install the new diaphragm, ensuring it is correctly seated and aligned.
8. Reassemble the fuel pump housing and tighten screws to the manufacturer's specified torque.
9. Mount the pump back onto the engine block and reconnect the fuel lines securely.
10. Reconnect the battery, prime the fuel system if necessary, and start the engine.
11. Inspect carefully for any fuel leaks around the pump and its connections before operating the vessel.

Troubleshooting & FAQ

Safety & Important Info

• Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended for safety and performance.

About Sea Sierra

• Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
• Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
• Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.