Carburetor Assembly for Tohatsu/Nissan/Mercury 15–20 HP 4-Stroke Outboards – Replaces 3BJ-03100-0, 853720T21, 8M0109535 and 5040597
Carburetor Assembly for Tohatsu/Nissan/Mercury 15–20 HP 4-Stroke Outboards – Replaces 3BJ-03100-0, 853720T21, 8M0109535 and 5040597 is backordered and will ship as soon as it is back in stock.
Worry-free returns
Worry-free returns
Shop with confidence. If you’re not completely satisfied, eligible items may be returned within the return window, provided they are unused and in original packaging.
If the return is due to our error or a defective item, we’ll make it right.
Please contact us before returning any item.
Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
International delivery times may vary due to customs processing.
Tracking information will be provided once your order ships.
Carburetor Assembly for Tohatsu/Nissan/Mercury 15–20 HP 4-Stroke Ou...
Carburetor Assembly for Tohatsu/Nissan/Mercury 15–20 HP 4-Stroke Outboards – Replaces 3BJ-03100-0, 853720T21, 8M0109535 and 5040597 is backordered and will ship as soon as it is back in stock.
Product Details
This is a complete aftermarket carburetor assembly for selected Tohatsu and Nissan 15–20 HP four-stroke outboard applications. It is listed as a replacement for Tohatsu and Nissan MFS20C/NSF20C four-stroke outboard engines, including the documented model-year ranges shown below. Cross-referenced applications may also include selected Mercury and Johnson/Evinrude four-stroke outboards that use the corresponding manufacturer part numbers.
This carburetor assembly replaces or cross-references Tohatsu part 3BJ-03100-0, Mercury parts 853720T21 and 8M0109535, and Johnson/Evinrude part 5040597. Confirm the number on your original carburetor and compare the images, connectors, mounting pattern and linkages before ordering.
- Complete carburetor assembly for the listed applications.
- Designed as an OEM-style aftermarket replacement for service and repair use.
- Die-cast aluminum housing for use in marine environments.
- Mounting gaskets are included as listed for this assembly.
Part Number Matrix
Use this matrix to compare the listed manufacturer and cross-reference numbers. A cross-reference alone does not confirm every model, year or serial-number application.
| Brand | Part Number |
|---|---|
| Tohatsu | 3BJ-03100-0 |
| Mercury | 853720T21 / 8M0109535 |
| Johnson/Evinrude | 5040597 |
Engine & Model Compatibility
Fitment should be confirmed by matching the original carburetor part number and the complete engine model information. The following applications are listed for this replacement:
| Brand | Model | Rated HP | Stroke | Years | Reference Part No. |
|---|---|---|---|---|---|
| Tohatsu | MFS20C | 20 | 4-Stroke | 2008–2014 | 3BJ-03100-0 |
| Nissan | NSF20C | 20 | 4-Stroke | 2009 | 3BJ-03100-0 |
Selected Mercury 15–20 HP and Johnson/Evinrude 20 HP four-stroke outboards may use the cross-referenced numbers below. Because complete model, year and serial-number boundaries are not documented here, verify the original part number and physical configuration before purchase.
| Brand | Model Scope | Rated HP | Stroke | Reference Part No. |
|---|---|---|---|---|
| Mercury | Selected models using the listed cross-reference | 15–20 | 4-Stroke | 853720T21 / 8M0109535 |
| Johnson/Evinrude | Selected models using the listed cross-reference | 20 | 4-Stroke | 5040597 |
Technical Specifications
- Product Type
- Carburetor assembly
- Application
- Selected 15–20 HP four-stroke outboard engines
- Fuel Type
- Gasoline
- Housing Material
- Die-cast aluminum
- Housing Color
- Silver/metallic
- Installation
- Replacement installation using the existing engine mounting configuration
- Warranty
- 1 year against manufacturing defects under normal use
- Included Installation Components
- Mounting gaskets as listed
What’s in the Box
- 1 × Carburetor assembly
- Mounting gaskets as listed for the assembly
No external fuel filter, fuel line, throttle cable, choke cable or additional engine components are included unless specifically shown or stated in the order details.
Installation Notes
- Disconnect the battery, shut off the fuel supply and allow the engine to cool before beginning work.
- Photograph or mark the positions of the fuel lines, throttle linkage, choke linkage and other connections before removal.
- Disconnect the fuel lines and control linkages from the original carburetor.
- Remove the nuts or bolts securing the carburetor to the intake manifold, then remove the original carburetor and gasket.
- Clean the mounting surface and inspect the intake area for debris, damage or fuel contamination.
- Install the supplied mounting gasket and replacement carburetor assembly in the original orientation.
- Tighten the fasteners evenly to the torque specified in the applicable engine service manual.
- Reconnect all fuel lines and control linkages, confirming that each connection is secure and moves freely.
- Restore the fuel supply and inspect all connections for leaks before starting the engine.
- Start the engine in a safe, well-ventilated location and check idle quality, throttle response and fuel leakage.
- Make only the adjustments permitted by the applicable engine service manual. Do not operate the engine if fuel leakage or abnormal operation is present.
Troubleshooting & FAQ
How can I confirm fitment for my Mercury or Johnson/Evinrude engine?
Match the number on your original carburetor to 853720T21, 8M0109535 or 5040597, then compare the engine model, horsepower, stroke and physical configuration. The cross-reference does not establish every model or serial-number range, so consult the engine service information when those details are unavailable.
Does this carburetor fit every 15–20 HP four-stroke outboard?
No. The listed horsepower and stroke are not sufficient by themselves to confirm fitment. Model, year, serial number, original part number, mounting arrangement and linkage configuration must agree.
Is adjustment needed after installation?
The assembly is intended for the listed applications, but idle speed or other service adjustments may be needed after installation depending on the engine and its condition. Follow the applicable owner’s or service manual and use the manufacturer’s specified procedures.
What symptoms can indicate a failing carburetor?
Possible symptoms include hard starting, rough idle, stalling, poor acceleration, black exhaust smoke and fuel leakage. These symptoms can also result from ignition, fuel-supply, ventilation or engine-compression problems, so diagnose the engine before replacing parts.
Does the assembly include a fuel filter?
No external fuel filter is included. If the existing filter is contaminated, damaged or due for service, replace it separately according to the engine manufacturer’s maintenance instructions.
Can I clean or rebuild my original carburetor instead?
Cleaning or rebuilding may be appropriate when the carburetor body and internal components are serviceable. Replacement is often preferable when components are worn, corroded, damaged or no longer seal correctly.
Is this an OEM part?
This listing is for an aftermarket replacement component, not a part manufactured by Tohatsu, Nissan, Mercury, Johnson or Evinrude. The manufacturer names and part numbers are used only to identify the intended application and cross-reference.
What are the shipping speeds and costs?
Standard shipping is free where offered. Typical transit time is 5–15 days for many regions, while available expedited services and their costs are shown at checkout and may vary by destination.
What is the warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal use. Returns are subject to the applicable return policy and normally require the item to be unused and in its original condition. Contact support with your order details for assistance.
Safety & Important Information
- Verify the original carburetor number, engine model, year, horsepower, stroke and physical configuration before ordering.
- Do not rely on horsepower alone to establish fitment.
- Inspect all fuel connections for leaks before operating the engine.
- This is an aftermarket replacement component and is not an original equipment manufacturer part.
- Professional installation is recommended if you are not familiar with marine fuel systems or outboard controls.
About Sea Sierra
- Pro-Grade Standards — We supply marine replacement parts designed for reliable service in demanding marine environments.
- Fast Global Fulfillment — Free standard delivery is available to most regions, with typical transit times of 5–15 days.
- Manufacturer-Direct Value — We work with manufacturing partners to provide replacement parts at competitive prices.
Payment & Security
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
