Mercury MerCruiser Quicksilver Diaphragm Kit 55278A1
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Mercury Quicksilver Diaphragm Kit – Part No. 55278A1
This is a genuine OEM Mercury Marine / Quicksilver diaphragm kit for MerCruiser carbureted engine applications. Diaphragm kits in this part number range are used in fuel pump assemblies, choke pull-off mechanisms, and vacuum-operated carburetor components on carbureted MerCruiser sterndrive and inboard engines. The A1 suffix designates the current revised kit specification. A failed or hardened diaphragm is a common cause of fuel delivery problems, hard starting, and rough running on carbureted engines — replacing the diaphragm kit restores proper fuel pump stroke or choke operation without replacing the entire assembly.
Part Details
- Part Number: 55278A1
- Brand: Mercury Marine / Quicksilver
- Official Product Type: Diaphragm Kit
- Revision: A1 — current production specification
- System: Fuel System — carburetor or fuel pump assembly
- Condition: New OEM
Compatible Applications
- MerCruiser carbureted sterndrive and inboard engines — specific assembly varies by model and serial number range
- Fuel pump diaphragm replacement on carbureted engine packages
- Choke pull-off or vacuum diaphragm replacement on Rochester and MerCarb carburetors
- Verify fitment using the Mercury parts diagram, carburetor model, and engine serial number before ordering
- Not applicable to EFI or MPI fuel-injected engines
Kit Contents
Contents vary by application but typically include one or more diaphragm membranes and associated sealing components. Confirm kit contents against the Mercury parts diagram for your specific assembly before ordering.
Installation Notes
- Relieve fuel system pressure and disconnect the fuel supply before disassembly
- Note the orientation of the diaphragm before removal — incorrect orientation will prevent proper operation
- Clean all mating surfaces and inspect the housing for cracks or corrosion before installing the new diaphragm
- Replace all gaskets and seals disturbed during disassembly
- Follow the Mercury service manual for reassembly sequence and torque specifications
- Check for leaks and verify correct operation before returning the engine to service
Service Interval
Inspect the diaphragm during annual carburetor service or any time fuel delivery problems, hard starting, or rough running are present. Replace immediately if the diaphragm shows cracking, hardening, pinhole leaks, or loss of flexibility. Diaphragms degrade over time from fuel exposure and heat cycling even without visible damage — replacement during a carburetor overhaul is recommended as a matter of course.
Parts Desk Insights
Best use case: Annual carburetor service, fuel pump rebuild, or targeted diagnosis of fuel delivery problems on carbureted MerCruiser engines. This kit is the correct path when the diaphragm is the failed component and the housing is still serviceable — significantly less expensive than replacing the entire fuel pump or carburetor assembly.
Common mistakes: Ordering a diaphragm kit without confirming the carburetor or fuel pump model — Mercury used several different diaphragm specifications across Rochester, MerCarb, and fuel pump assemblies that are not interchangeable. Also confirm the engine is carbureted: EFI and MPI engines do not use diaphragm-type fuel pumps or choke pull-offs. If the diaphragm has failed due to ethanol fuel damage, inspect the entire carburetor for related deterioration before reassembly.
Related Parts
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
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