Mercury 3.5HP 2-Stroke Outboard Engine Parts

(8 products)

This page is dedicated to Mercury 2-Stroke 3.5HP outboard engines. Use it to find compatible parts and practical service information. Below you’ll find maintenance tips, common replacement parts, and troubleshooting guidance. You can also browse our main Mercury collection. Scroll to the bottom of this page to start browsing parts for this engine, and remember you can use the Filter & Sort controls on the collection page to narrow results by horsepower, year range, and part category/section.

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How to Identify Your 3.5HP Model

Find the nameplate/serial plate on the transom clamp bracket (usually on the port side). Record the full serial number and any model code.
Model suffixes often indicate shaft length (short ≈ 15", long ≈ 20") and sometimes region or revision. Match these to parts notes where applicable.
This is a 2‑Stroke engine: look for an integral top‑mount fuel tank, recoil starter, and a single carburetor. Verify 2‑Stroke vs. 4‑Stroke before ordering parts.
If your motor has a long shaft, the driveshaft, water tube, and certain gear housing components differ from short‑shaft versions—confirm before purchase.

Engine Overview

Mercury 3.5HP 2‑Stroke (Single‑Cylinder)

Feature	Description
Configuration	Single‑cylinder, carbureted 2‑Stroke with recoil start and integral fuel tank.
Common Models	3.5HP 2‑Stroke short‑shaft and long‑shaft variants across multiple serial ranges.
Advantages	Lightweight, simple mechanics, easy to service, reliable trolling power.
Notes	Some parts vary by serial range and shaft length. Cooling and gearcase parts may differ between short and long shaft. Always match parts using your serial plate details.

Routine Maintenance & Service Parts

Intervals below are general guidelines for small 2‑Stroke outboards. Always follow your official service manual and adjust for heavy use, sandy/silty water, or storage conditions.

Item	Interval*	Remarks	Parts Link
Gear oil (lower unit)	Every 100 hrs or annually	Inspect for water (milky oil) and metal. Replace drain screw gaskets if needed.	Mercury Lower Unit Seal Kits
Spark plugs	Inspect every 50 hrs; replace 100 hrs/annually	Use the specified heat range; set gap per manual to maintain easy starting.	Spark Plugs
Fuel filter (inline)	Inspect 50 hrs; replace 100 hrs/annually	Replace more often with ethanol fuel or if debris is present.	Fuel Filters
Water pump impeller/kit	Every 2 seasons or 200 hrs (sooner for sandy water)	Critical for cooling on small 2‑Strokes; replace at first sign of weak tell‑tale stream.	Mercury Water Pump Repair Kits
Anodes (gearcase/trim tab)	Inspect 50 hrs; replace when 50% worn	Use the correct alloy for your waters (zinc, aluminum, or magnesium).	Anodes
Fuel/oil premix (2‑Stroke)	Every refuel	Follow the manual’s ratio (commonly 50:1 TC‑W3). Use fresh, ethanol‑free fuel where possible.	Mercury Outboard Parts

Frequently Used Parts Categories

Routine Service: Mercury Outboard Parts
Cooling System: Mercury Water Pump Repair Kits
Lower Unit / Gearcase: Mercury Lower Unit Seal Kits
Fuel System: Fuel Filters
Ignition / Electrical: Spark Plugs
Propulsion: Propellers
Stabilization & Handling: Outboard Hydrofoil Stabilizers

Common Symptoms & Quick Checks

Symptom	Check First	Related Parts
Weak tell‑tale stream or overheat	Inspect intake screen for debris; verify tell‑tale hose is clear; check impeller condition.	Water pump kit, intake screen, gaskets
Poor acceleration / power loss	Confirm fresh fuel and correct premix; check spark plug; inspect propeller for damage or excessive pitch.	Spark plug, inline fuel filter, carb service parts, propeller
Hard starting / rough idle	Verify choke/enrichment works; clean carb jets; check for air leaks at fuel lines.	Fuel filter, fuel line clamps, carb gaskets/needle & seat
Excessive smoke (2‑Stroke)	Confirm correct oil ratio; ensure choke is opening; check for flooded carburetor.	Spark plug, carburetor service parts
Gearcase noise / metal in gear oil	Check gear oil for water/metal; inspect prop shaft for fishing line; pressure test seals.	Lower unit seal kit, drain/fill gaskets, bearings

FAQs

Are parts interchangeable across different years or serial ranges?

Some components are shared, but many small 2‑Stroke items (cooling, gearcase, and carburetor parts) vary by serial range and shaft length. Always verify using your serial plate before ordering.

When should I replace the water pump impeller?

As a preventative measure, replace every two seasons or ~200 hours—sooner if the tell‑tale weakens, you ingest sand/silt, or the motor overheats.

How often should I change lower unit gear oil?

Every 100 hours or annually. Inspect for water (milky appearance) and metal particles; address seal issues immediately if contamination is found.

What information helps confirm part compatibility?

Provide clear photos of the nameplate with serial/model code, shaft length (short/long), and the specific part area (e.g., carburetor, gear housing). This ensures the correct parts for your exact configuration.

Ready to find the right components? Browse the main Mercury collection and use Filter & Sort to narrow by horsepower, year, and model.

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If you’re unsure about your model, send us a photo of the nameplate and the part you need and we’ll help verify compatibility.