3H6-04000-7 Mechanical Fuel Pump Assembly

Mechanical Fuel Pump — Compatible with select Tohatsu Nissan Mercury Mariner Four-Stroke

Which pump is this?

This is a complete mechanical diaphragm fuel-pump assembly for small carbureted four-stroke outboards. It replaces Tohatsu / Nissan 3H6-04000-7 (current), 3H6-04000-4, and 3H6-04000-3, and Mercury / Mariner 803529T06 (current) and 803529T03 (prior). Compatible with select Tohatsu / Nissan MFS4 / MFS5 / MFS6 and MFS8A3 / MFS9.8A3 four-stroke platforms, and with Mercury / Mariner 4, 5, and 6 HP carb four-stroke engines in the serial bands in the table. Pulse comes from the crankcase. It is not an electric / VST high-pressure pump, not a cooling water-pump impeller, and not a 2-stroke pump.

Signs yours is due

• Hard hot restart on a 4–6 HP four-stroke that used to fire immediately — the tiny diaphragm can take a set or weep into the pulse cavity.
• Carburetor bowl runs dry after a short sit, or idle dies when you tilt the motor — fuel is not being pulled from the tank.
• Fuel smell or wetness at the pump body / pulse gasket, or a cracked plastic cover on this small assembly.
• Not a cooling problem: steam, overheat alarm, or no tell-tale is the water-pump impeller, not this fuel pump.

Will it fit?

Compatible with the Tohatsu / Nissan four-stroke models and the Mercury / Mariner 4 / 5 / 6 HP carb serial ranges listed below. MFS4C / 5C / 6C books use 3H6-04000-4 on undated pages and 3H6-04000-7 on 2012–2014 dated books — same pump family, confirm the stamp on the pump you remove. Mercury 4–6 HP carb uses 803529T06 on current bands and 803529T03 on overlapping older catalog pages. Horsepower name alone does not prove fit. Same 4 / 5 / 6 HP badge shipped different pumps.

Engine horsepower alone does not prove fit. Match the number stamped on the pump you remove to the OEM column.

Every row is from this SKU fitment workbook (21 rows after empty-line filter). Same horsepower name shipped different pumps.

OEM and swap numbers

OEM / predecessor numbers keep the engine-brand column. Aftermarket cross-refs are numbers only.

Wrong part

• NOT 803529T07 — that is the 8 / 9.9 HP 209cc Mercury / Mariner family, a different pump.
• NOT 3H8-04000-1 / 803529T04 — larger four-stroke family (neighbor SKU 24FP095), not this small carb pump.
• NOT a 2-stroke fuel pump (356-04000-1 / 6E5-24410 and similar) and NOT a water-pump impeller.
• NOT kit 26FFK028 — that SKU adds a filter. This page is the pump assembly only.

What ships

One complete mechanical fuel-pump assembly. No hose, no fuel filter, no carburetor, no rebuild kit, no bolts unless they are staked on the pump you see in the photos.

Often replaced together

While the cowl is off, inspect the fuel-filter element and the primer bulb. Those are sold separately. If you need the pump plus filter as a set, that is a different GHMarine SKU (26FFK family), not this page.

Install

Shut the tank, relieve pressure, and catch fuel. Photograph the pulse hose and fuel-line routing before you pull the old pump. Remove the two (typical) flange screws, lift the pump, and scrape the old gasket off the crankcase pad. Fit a new gasket dry unless your shop manual calls for a thin sealant. Seat the pulse port on the crankcase passage — a pinched gasket here mimics a dead pump. Snug the screws evenly; do not crush the cover. Prime the bulb, check for leaks, then run on muffs. If it still will not pick up fuel, check the tank vent and the bulb before you blame the new pump.

Frequently Asked Questions

Will this fit my 8 / 9.8 HP Tohatsu four-stroke?

MFS8A3 / MFS9.8A3 four-stroke rows are in the table with 3H6-04000-4 or 3H6-04000-7. Compatible with those catalog platforms only — not Mercury 8 / 9.9 HP 803529T07. Match the stamp on the pump you remove.

Will this fit my Mercury 4 / 5 / 6 HP four-stroke?

Compatible with carb 4 / 5 / 6 HP four-stroke engines in the serial bands in the table (803529T06 current, 803529T03 prior). Horsepower on the cowl is not enough. Read the serial on the midsection or swivel bracket.

Is this an electric pump?

No. Mechanical diaphragm, crankcase pulse. If your engine uses a VST / electric high-pressure pump, this is the wrong part.

What is in the box?

One complete mechanical fuel-pump assembly. No extra hose, filter, or carburetor kit.

How do I know the old pump is bad?

Hard hot restart, dry carb bowl, fuel weep at the body, or a cracked cover. Overheat / no tell-tale is the water pump, not this part.

Please note

Aftermarket fuel pump by GHMarine. Not affiliated with the engine brands named above. «Compatible with», «Replaces», and cross-ref numbers mean this part is built to work like the originals listed — always confirm the stamp on the removed pump, the engine model, and the serial range before you order. This page is the pump only, not a multi-part kit.