Fuel Pump Diaphragm Kit for Mercury, Mariner and Force 30–275 HP Outboards — Replaces 21-857005A1 and 21-42990A10
Fuel Pump Diaphragm Kit for Mercury, Mariner and Force 30–275 HP Outboards — Replaces 21-857005A1 and 21-42990A10 is backordered and will ship as soon as it is back in stock.
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Fuel Pump Diaphragm Kit for Mercury, Mariner and Force 30–275 HP Ou...
Fuel Pump Diaphragm Kit for Mercury, Mariner and Force 30–275 HP Outboards — Replaces 21-857005A1 and 21-42990A10 is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket fuel pump diaphragm kit is designed for rebuilding or servicing compatible mechanical fuel pumps on selected Mercury, Mariner and Force outboard engines. It is listed for gasoline fuel systems and is intended to restore fuel-pump operation when the original diaphragm has become cracked, stiff, worn or damaged.
The kit is associated with Mercury and Chrysler Force fuel-pump applications using the documented references 21-857005A1 and 21-42990A10. It is also cross-referenced to Sierra 18-7817, GLM 40290 and EMP 1399-39020. These numbers are application references, not a claim that the product is manufactured by Mercury, Mariner, Chrysler, Sierra, GLM or EMP.
- Fuel-pump diaphragm rebuild kit for one compatible fuel pump.
- Designed as a replacement for the original diaphragm assembly.
- Compatible with gasoline fuel systems.
- Application coverage includes selected Mercury, Mariner and Force outboards from approximately 30 to 275 HP, subject to model, pump design and serial-number conditions.
Part Number Cross-Reference
Confirm the number stamped on your original fuel-pump assembly and verify the engine model and serial range before ordering.
| Brand or source | Reference number | Reference type |
|---|---|---|
| Mercury / Chrysler Force | 21-857005A1 | OEM application reference |
| Mercury / Chrysler Force | 21-42990A10 | OEM application reference |
| Mercury | 21-42990A7 | Related application reference |
| Mercury | 21-42990A8 | Related application reference |
| Mercury | 21-42990A9 | Related application reference |
| Sierra | 18-7817 | Aftermarket cross-reference |
| GLM | 40290 | Aftermarket cross-reference |
| EMP | 1399-39020 | Aftermarket cross-reference |
Engine and Model Compatibility
The documented application range covers selected Mercury and Mariner 30–275 HP two-stroke outboards and selected Force 40–150 HP two-stroke outboards. Some Mercury or Mariner four-stroke engines may use a compatible square or triangular fuel-pump design, but four-stroke fitment is not universal.
Fuel-pump design, model year and serial number must be considered together. The examples below are application leads from the related fuel-pump catalog data; they do not replace confirmation against the engine identification label and the original pump.
| Brand | Model or horsepower | Stroke | Year or serial condition | Related reference |
|---|---|---|---|---|
| Mercury | 30, 2-cylinder | 2-Stroke | Serial 0G055314–0G760299 | 21-857005A1 |
| Mercury | 30, 2-cylinder | 2-Stroke | Serial 0G760300–0T979999 | 21-857005A1 |
| Mercury | 30, 2-cylinder | 2-Stroke | Serial 0T980000–0T999999 | 21-857005A1 |
| Mercury | 30, 2-cylinder | 2-Stroke | Serial 1B000001 and up | 21-857005A1 |
| Mercury | 35–125 HP | 2-Stroke | Selected model and serial ranges | 21-42990A10 |
| Mercury | 135–275 HP | 2-Stroke | Selected V-series and high-output models | 21-42990A10 |
| Mariner | 75–275 HP | 2-Stroke | Selected model and serial ranges | 21-42990A10 |
| Force | 40–150 HP | 2-Stroke | Selected 1991–1999 applications | 21-42990A10 |
Important: A horsepower match by itself does not confirm fitment. Compare the pump housing, diaphragm layout, cover and mounting arrangement with the original assembly. If your engine has a different pump design or falls outside the listed serial range, this kit may not fit.
Technical Specifications
- Product type
- Fuel pump diaphragm rebuild kit
- Application
- Selected Mercury, Mariner and Force outboard fuel pumps
- Fuel type
- Gasoline
- Typical engine range
- Mercury and Mariner 30–275 HP; selected Force 40–150 HP applications
- Installation
- Replacement of the compatible fuel-pump diaphragm assembly
- Product status
- Aftermarket replacement; not an OEM-manufactured component
What's in the Box
- 1 × spring
- 1 × cap
The package contents are limited to the components supplied with this listing. The original pump's gaskets, check valves, fasteners and other hardware are not stated as included unless shown in the package contents above.
Installation Notes
- Work in a well-ventilated area away from flames, sparks and ignition sources.
- Disconnect the battery and relieve fuel-system pressure before servicing the pump.
- Identify the fuel-pump design and note the orientation of the original diaphragm, spring and cap.
- Remove the pump cover carefully and retain any reusable hardware that is not supplied with this kit.
- Inspect the pump body, cover, valves, sealing surfaces and fuel lines for wear or contamination.
- Install the replacement components in the same orientation as the original parts.
- Reassemble the pump using the engine manufacturer's specified tightening procedure. Do not overtighten the cover screws.
- Reconnect the fuel lines, prime the system and inspect carefully for leaks before starting the engine.
- After starting, verify stable fuel delivery and recheck for leakage before returning the boat to service.
Professional installation is recommended because gasoline leaks and incorrect fuel-pump assembly can create fire, engine-damage and personal-safety hazards.
Troubleshooting and FAQ
How do I confirm that this kit fits my engine?
Compare the original fuel-pump reference, pump shape, diaphragm arrangement and engine serial number with the compatibility information above. Do not rely on horsepower alone.
Will this kit fit every Mercury or Mariner four-stroke engine?
No. Four-stroke fitment is limited to selected engines using the compatible fuel-pump design. Inspect the pump and verify the exact application before ordering.
What symptoms can indicate a worn fuel-pump diaphragm?
Possible symptoms include hard starting, rough idle, hesitation during acceleration, fuel starvation at higher speed and fuel leakage around the pump. These symptoms can also be caused by clogged filters, damaged fuel lines, carburetor problems or other fuel-system faults.
Does the kit include every gasket and check valve needed for a rebuild?
The listed package contents are one spring and one cap. Reuse or replace other pump components only as appropriate for your specific pump and only with parts confirmed for that application.
Is this an OEM Mercury or Force part?
No. This is an aftermarket replacement kit. The Mercury, Chrysler Force, Sierra, GLM and EMP numbers are used only as application or cross-reference numbers.
Can this kit repair an engine oil leak?
No. This product is intended for fuel-pump diaphragm service and is not an oil-seal or crankcase repair part.
Safety and Important Information
- Verify the original pump design, application reference and serial range before ordering.
- Do not install the kit if the supplied parts differ from the original components or the pump diagram.
- Use only with compatible gasoline fuel systems.
- Inspect for fuel leaks before and after starting the engine.
- This is an aftermarket replacement and is not manufactured by Mercury, Mariner, Chrysler, Sierra, GLM or EMP.
About Sea Sierra
- Marine replacement parts — Practical aftermarket components for common service and repair applications.
- Application-focused listings — Cross-reference numbers and fitment conditions are provided to help you compare the replacement with your original part.
- Support for accurate ordering — Verify the model, serial number and component design before installation.
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