Outboard Primer Bulb 8mm 5/16in One-Way Fuel Line MMS-4280
mms-4280
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8mm Outboard Fuel Primer Bulb
One-way bulb for 5/16in low-pressure fuel hose
A large inline primer bulb for compatible outboard fuel systems using 8 mm (5/16 in) ID hose. The internal check valves allow manual priming from the tank towards the engine.
Key Features
- For 8 mm (5/16 in) fuel hose
- One-way internal check valves
- Moulded arrow identifies flow direction
- Large bulb body for manual priming
- Clamps are required but not included
Technical Specs
| Hose size | 8 mm (5/16 in) ID |
| Part type | Inline primer bulb |
| Flow direction | Arrow points towards engine |
| System type | Low-pressure petrol feed |
| Clamps | Not included |
| 4Boats SKU | mms-4280 |
Compatibility / Fitment Guide
This bulb is not selected by engine horsepower. It fits a low-pressure outboard fuel line only when the hose is 8 mm (5/16 in) ID and can be clamped correctly over both bulb barbs.
| Hose check | Read the hose marking or measure its internal diameter; 10 mm (3/8 in) and 6 mm (1/4 in) hose require different bulbs. |
| Orientation | Cut into the feed line and install the arrow tank → engine. Reversed installation prevents correct priming. |
| Position | Place where the bulb can be reached, supported and inspected, away from heat, sharp edges and control-linkage movement. |
| Clamping | Use two correctly sized stainless fuel-hose clamps. Do not reuse damaged hose ends or overtighten until the barb cuts the hose. |
| Not suitable for | High-pressure EFI delivery lines, diesel unless specifically approved, pressurised tank systems, or hose of a different internal diameter. |
Part Number Cross Reference
| Size reference | 8 mm / 5/16 in |
| Supplier / 4Boats SKU | mms-4280 |
No engine-specific OEM number is claimed. Compatibility is established by hose size, pressure side and installation requirements.
Frequently Asked Questions
Does it fit all outboards?
No. It fits compatible low-pressure systems using 8 mm ID hose.
Are clamps included?
No.
Why will the bulb not draw fuel?
Check arrow direction, tank vent, connector seals, hose leaks and whether the bulb is being held with its outlet end raised where the engine maker recommends.
Can it replace a 10 mm bulb?
No, not without changing to the correct hose and fittings.
Prime and leak-test the system before starting the engine. Fuel-system work must be carried out in a ventilated area with all ignition sources removed.
For the products under £150 the shipping is £6.99.
Free delivery for most items over £150.
