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

Fuel Pump Diaphragm Kit – Fits Mercury/Mariner & Force 30-275 HP

This fuel pump diaphragm kit provides a reliable replacement solution for a wide range of Mercury, Mariner, and Force outboard engines. It is designed to restore fuel system performance in 2-stroke and 4-stroke models, specifically fitting Mercury/Mariner 30-275 HP (1978–1999) and Force/Chrysler 40-150 HP (1991–1999) outboards. For 4-stroke applications, please verify that your engine has a square or triangular fuel pump.

Engineered as a direct replacement, this kit services fuel pumps corresponding to multiple part numbers, ensuring broad compatibility across various models and years. It addresses common fuel delivery issues caused by worn or failed diaphragms.

• Direct Installation: Designed to replace the original diaphragm and gasket without modifications.
• Quality Manufacturing: Produced in an ISO9002 certified factory to meet or exceed OEM specifications.
• Complete Kit: Includes the necessary diaphragm and base gasket for a standard service.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Mercury/Mariner Outboards

Force/Chrysler Outboards

Confirm your engine model/year in the table below.

Technical Specifications

Package Contents

• 1 x Fuel Pump Diaphragm Kit (Replaces 21-857005A1)
• 1 x Base Gasket (Sierra 18-0970)

Installation Guide

1. Safety First: Before starting, ensure the engine is off, cool, and disconnected from the battery. Work in a well-ventilated area away from sparks or open flames.
2. Access the Fuel Pump: Remove the engine cowling to locate the fuel pump assembly. Note the routing of the inlet and outlet fuel lines.
3. Disconnect Fuel Lines: Place a rag under the fuel line connections to catch any residual fuel. Carefully disconnect the fuel lines from the pump.
4. Remove the Fuel Pump: Unscrew the mounting bolts that secure the fuel pump to the engine block and remove the pump. Note the position of the old gasket.
5. Disassemble the Pump: Place the pump on a clean workbench. Carefully unscrew the housing screws to separate the pump body and access the old diaphragm.
6. Replace the Diaphragm: Remove the old diaphragm, noting its orientation. Install the new diaphragm from the kit in the same position.
7. Reassemble the Pump: Ensure all internal components are clean and correctly seated. Reassemble the pump housing and tighten the screws evenly.
8. Install the New Gasket and Pump: Clean the mounting surface on the engine block. Place the new base gasket in position and mount the reassembled fuel pump, tightening the bolts to the manufacturer's specified torque.
9. Reconnect Fuel Lines: Securely reattach the inlet and outlet fuel lines to the correct ports on the pump.
10. Final Checks: Reconnect the battery. Prime the fuel system using the primer bulb until firm. Start the engine and carefully inspect the pump and fuel lines for any leaks.

Troubleshooting & FAQ

How do I confirm this kit fits my engine?

To ensure compatibility, compare your engine's model, horsepower, and year against the lists provided. For Mercury/Mariner models, it is crucial to also verify your engine's serial number falls within the specified range. For 4-stroke engines, visually confirm you have a square or triangle-shaped fuel pump, as this kit is designed for those types.

What are the signs my fuel pump diaphragm is failing?

Common symptoms of a bad diaphragm include the engine running rough, stalling at low speeds, difficulty starting, or a noticeable decrease in top-end performance. You may also see or smell fuel leaking from the fuel pump's weep hole or seams, which indicates an internal rupture.

What parts does this kit directly replace?

This is an aftermarket kit that replaces OEM Mercury part number 21-857005A1 and its predecessors. It also serves as a cross-replacement for other aftermarket parts, including Sierra 18-7817 and GLM 40290. Please see the cross-reference table for a complete list.

OEM vs. Aftermarket?

This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?

We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?

This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.