Carburetor Assembly – Fits Tohatsu/Mercury 15-20 HP 4-Stroke (Replaces Tohatsu 3BJ-03100-0, Mercury 853720T21/8M0109535, Johnson/Evinrude 5040597)
Carburetor Assembly – Fits Tohatsu/Mercury 15-20 HP 4-Stroke (Replaces Tohatsu 3BJ-03100-0, Mercury 853720T21/8M0109535, Johnson/Evinrude 5040597) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Carburetor Assembly – Fits Tohatsu/Mercury 15-20 HP 4-Stroke (Repla...
Product Details
This is a complete Carburetor Assembly – Fits Tohatsu/Mercury 15-20 HP 4-Stroke (Replaces 3BJ-03100-0), designed as a direct-fit replacement for Tohatsu and Nissan MFS20C/NSF20C 4-stroke 15-20 HP outboard engines from 2008–2014. It is also compatible with equivalent Mercury and certain Johnson/Evinrude 4-stroke 15-20 HP outboards.
This assembly directly replaces Tohatsu part 3BJ-03100-0, Mercury parts 853720T21 and 8M0109535, and Johnson/Evinrude part 5040597.
- Engineered as a direct OEM-style replacement for easy installation.
- Constructed from durable die-cast aluminum for longevity in marine environments.
- Includes necessary mounting gaskets for a complete installation.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Tohatsu | 3BJ-03100-0 |
| Mercury | 853720T21 / 8M0109535 |
| Johnson/Evinrude | 5040597 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
Fitment for Tohatsu MFS20C (2008–2014) and Nissan NSF20C (2009) is confirmed.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. |
|---|---|---|---|---|---|
| Tohatsu | MFS20C | 20 | 4-Stroke | 2008–2014 | 3BJ-03100-0 |
| Nissan | NSF20C | 20 | 4-Stroke | 2009 | 3BJ-03100-0 |
This part is a known replacement for various Mercury 15-20 HP and Johnson/Evinrude 20 HP 4-stroke models that use the cross-referenced part numbers. Please verify the part number on your original carburetor before ordering.
| Brand | Model | Rated HP | Stroke | OEM Part No. |
|---|---|---|---|---|
| Mercury | Various 15-20 HP Models | 15-20 | 4-Stroke | 853720T21 / 8M0109535 |
| Johnson/Evinrude | Various 20 HP Models | 20 | 4-Stroke | 5040597 |
Technical Specs
- Product Type
- Carburetor Assembly
- Installation
- Direct OEM replacement
- Fuel Type
- Gasoline
- Housing Material
- Die-cast aluminum
- Housing Color
- Silver/metallic
- Warranty
- 1 year (FridayParts)
- Other Technical Attributes
- Includes necessary mounting gaskets
What’s in the Box
- 1 x Carburetor Assembly (Replaces 3BJ-03100-0)
Installation Notes
- Disconnect the battery and shut off the fuel supply to the engine.
- Carefully disconnect the fuel lines and any throttle or choke linkages from the old carburetor. Note their positions for reassembly.
- Remove the nuts or bolts securing the carburetor to the intake manifold.
- Remove the old carburetor and gasket. Clean the mounting surface on the manifold thoroughly.
- Install the new gasket and mount the new carburetor assembly.
- Tighten the mounting nuts/bolts evenly to the manufacturer's specified torque.
- Reconnect the fuel lines and all linkages.
- Turn the fuel supply back on and check for any leaks.
- Reconnect the battery.
- Start the engine and check for smooth idling. Adjust idle speed if necessary according to your engine's service manual.
Troubleshooting & FAQ
How can I be sure this carburetor fits my Mercury or Johnson/Evinrude engine?
The best way to confirm fitment is to match the part number from your original carburetor to one of the cross-references listed: 853720T21, 8M0109535 (Mercury), or 5040597 (Johnson/Evinrude). While this part is known to fit many 15-20HP models from these brands, model-specific year ranges are not fully documented. Always verify by part number.
Is any adjustment needed after installation?
This carburetor is designed to work out-of-the-box for the specified Tohatsu/Nissan models. However, minor idle speed adjustment may be necessary depending on your specific engine's condition and local altitude. Refer to your owner's manual for adjustment procedures.
What are the signs my old carburetor is failing?
Common symptoms of a faulty carburetor include difficulty starting, rough idling, engine stalling, poor acceleration, black smoke from the exhaust, and fuel leaks. If you notice these issues, a carburetor replacement may be needed.
Does this carburetor include a new fuel filter?
This assembly does not include an external fuel filter. It's highly recommended to replace your engine's fuel filter at the same time you replace the carburetor to prevent contaminants from damaging the new part.
Can I clean my old carburetor instead of replacing it?
Cleaning and rebuilding a carburetor is possible with a rebuild kit, but it can be complex and may not solve issues related to internal wear or warped components. A full replacement assembly is often a more reliable and time-saving solution.
What is the difference between OEM and aftermarket parts?
This listing is an aftermarket replacement, not an original equipment manufacturer (OEM) part. It is built to OEM-level specifications with comparable materials and functionality but at a more accessible price point. Our parts are manufactured in an ISO 9002 facility and are batch-inspected for quality and consistency.
What are your shipping speeds and costs?
We ship worldwide quickly, with a typical transit time of 5–15 days for most regions. Standard shipping is free. If available for your location, expedited shipping options and their costs will be presented at checkout.
What is the warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in their original condition. See our full policy page or reach out for detailed instructions.
Safety & Important Info
- Verify images and specifications against your original part before ordering. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement component, not an OEM part.
- Professional installation is recommended for optimal safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world reliability in marine conditions.
- Fast Global Fulfillment — We offer free standard delivery to most regions, with an average transit time of 5–15 days.
- Manufacturer-Direct Value — By working directly with manufacturers, we provide fair pricing without compromising on materials or quality control.
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