Description
Fuel Pump Diaphragm & Washer Kit for Mercury/Mariner Outboard
The iFJF 18-7817 fuel pump rebuild kit restores proper fuel delivery for your Mercury or Mariner outboard engine. This kit replaces the critical diaphragm and check valves inside the mechanical pulse-style fuel pump — the components most prone to wear and ethanol-related deterioration. Replaces Mercury OEM 21-857005A1 and Sierra Marine 18-7817.
Key Features
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Complete Rebuild Kit: Includes fuel pump diaphragm, check valves, gaskets, and washers — everything needed to restore a mechanical pulse fuel pump.
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Ethanol-Ready Diaphragm: Upgraded elastomer material resists stiffening, cracking, and perforation caused by ethanol-blended fuels.
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Restores Fuel Pressure: Fixes weak fuel delivery, hard starting after sitting, and engine stalling under load caused by a failing diaphragm.
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Direct OEM Replacement: Manufactured to match Mercury/Mariner OEM specifications for pulse pump dimensions and flow rates.
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Cost-Saving Alternative: A complete OEM fuel pump assembly costs $80-150+. This rebuild kit achieves the same result at a fraction of the cost.
Cross-Reference / Interchange
| Brand |
Part Number |
| Sierra Marine |
18-7817 |
| Mercury / Mariner OEM |
21-857005A1 |
Signs of a Failing Fuel Pump Diaphragm
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Hard starting after sitting: Fuel drains back to the tank overnight — requires excessive cranking to re-prime.
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Engine stalls under load: Pump can't maintain fuel volume at higher RPM/load demands.
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Fuel in the pulse line: A perforated diaphragm allows fuel to enter the crankcase pulse line (dangerous — can dilute engine oil).
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Surging at cruise speed: Inconsistent fuel pressure causes RPM fluctuations.
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Visible cracking on diaphragm: Upon inspection, the rubber is stiff, cracked, or has pinholes.
Frequently Asked Questions
Q: Does this kit fit all Mercury/Mariner outboards?
A: This kit is designed for mechanical pulse-style fuel pumps found on many Mercury/Mariner 2-stroke outboards. Verify your pump matches OEM number 21-857005A1 before ordering. Not compatible with electric fuel pump systems.
Q: Can I rebuild the pump without removing it from the engine?
A: It's possible but not recommended. The pump is typically held by 2 bolts and the fuel lines. Removing it allows you to clean the mating surfaces properly and inspect the pulse port for blockages.
Q: What tools are needed?
A: Basic hand tools — Phillips screwdriver, flathead for prying, and a socket or wrench for the mounting bolts (typically 10mm or 3/8"). A pick tool helps remove old gasket material.
Q: How often should I rebuild the fuel pump?
A: As preventative maintenance, every 3-5 years if using ethanol fuel, or when symptoms of failure appear. If you run ethanol-free marine fuel, the diaphragm can last 8-10+ years.
Q: Is this kit compatible with fuel-injected outboards?
A: No. Fuel-injected outboards use high-pressure electric pumps. This kit is only for mechanical pulse pumps on carbureted 2-stroke engines.
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