Mercury Racing 15" ROS Mid-Section Saddle & Swivel Pin Assembly Exploded View Diagram Mercury Racing 15" ROS Mid-Section Clamp Brackets & Single Ram Trim Cylinder Assembly Exploded View Diagram Mercury Racing 15" ROS Mid-Section One-Piece Tuner Exhaust Plate & Smooth Back Exhaust Can Housing Assembly Exploded View Diagram The Mercury Racing 2.5 EFI ROS (Race Offshore) is a high-performance outboard engine renowned for its exceptional power-to-weight ratio and race-ready durability. Generating over 300 horsepower at 9,000 RPM and weighing approximately 375 lbs, it is a powerhouse in offshore racing, offering advanced innovations such as a lightweight aluminum flywheel, O-ring sealed cylinder heads for efficient heat transfer, and Electronic Fuel Injection (EFI) for precise throttle response. Paired with the precision-engineered 15-inch midsection, this engine delivers unmatched handling, acceleration, and control in competitive environments. The 15-inch midsection is a critical component that lowers the engine's center of gravity, enhancing balance and maneuverability during high-speed operation. Its design includes three key assemblies. First is the ROS Smooth Back Exhaust Housing Can, optimized for high exhaust flow with minimal backpressure. It features internal cooling jackets for heat dissipation and lightweight construction to reduce overall engine weight. Next, the Clamp Bracket Assemblies provide a robust connection between the engine and the transom, with heavy-duty brackets, a swivel mechanism for trim adjustments, and solid mounts for enhanced control. Finally, the Saddle Assembly with Single Ram Trim Cylinder delivers smooth, powerful trim adjustments through a compact, lightweight design, ensuring superior performance under demanding conditions. These components come with free exploded view diagrams, making them invaluable for racers and mechanics alike. The diagrams illustrate the ROS Smooth Back Exhaust Housing Can, Clamp Bracket Assemblies, and Saddle Assembly, offering detailed insights into their assembly and maintenance. Whether it’s outboard drag racing or offshore endurance events, the Mercury Racing 2.5 EFI ROS stands out with its high-performance racing applications, customizable configurations, and modular midsection design. This engine is more than a machine—it’s a testament to precision engineering, offering power, versatility, and reliability to racers who demand the best.

A "burnt" stator  is a common problem that can lead to serious engine trouble if left unaddressed. In this article, we’ll dive into the most common causes of stator burnout and what you can do to prevent CDI ignition failure and further costly repairs. 1. Overheating and Stator Damage One of the leading causes of a burnt stator  in Mercury outboard motors  is its gotten old and internal and or external wires have become compromised. If your motor experiences overheating this can cause a new stator to become "old" more quickly. If your engine runs too hot, the stator’s windings can become damaged, eventually leading to failure. Overheating can stem from various issues, such as: • Faulty water pump • Clogged cooling passages • Malfunctioning thermostat Make sure your cooling system is functioning properly to prevent stator damage. 2. Voltage Regulator or Rectifier Failure A defective voltage regulator  or rectifier can cause excessive voltage to flow through the stator, leading to overheating and burning. This is a common cause of CDI ignition failure  in outboards. Regularly inspect the regulator and rectifier to ensure they are operating within normal voltage ranges. 3. Moisture Intrusion and Corrosion Saltwater environments or poor weather conditions can cause corrosion on your outboard stator  and other electrical components. When moisture gets into the system, it can cause short circuits, leading to a burnt stator. Inspect your electrical system for signs of corrosion, especially if you frequently boat in saltwater or humid environments. 4. Shorted or Grounded Wiring Wiring issues  are another frequent cause of stator failure. Shorts in the wiring harness or improper grounding can lead to electrical imbalances, causing the stator to overheat and burn out. Check for chafed or frayed wires and ensure tight and secure connections. 5. Overloading the Charging System Overloading the charging system  by running too many accessories or having failing batteries can cause your stator to work harder than it’s designed to. This extra strain can eventually lead to stator burnout  in your Mercury outboard . 6. Loose or Corroded Connections Poor electrical connections, including loose or corroded wires, can result in high resistance in the charging system. This can cause the stator to overheat, leading to a burnt stator . Regularly check and clean all connections to maintain proper current flow. 7. Faulty or Low-Quality Stator Sometimes, a burnt stator  is simply the result of poor manufacturing. Low-quality or faulty replacement stators may fail prematurely, even under normal operating conditions. Always use high-quality parts when repairing or replacing your stator. Bad Cell in your Battery A bad cell in the battery can also cause increased or higher resistance in the circuit. This forces the stator to push more current and you will see the voltage increase to 16 or 17 volts, more than the system is designed to handle, further straining it and eventually leading to failure. AGM batteries are notorious for these failures. If you’re experiencing repeated stator failures  or CDI ignition issues , it’s helpful to diagnose the root cause. Regular maintenance and inspections of the cooling system, wiring, and voltage regulation components can help prevent further damage to your outboard’s electrical system. Preventative care will save you from the frustration of a burnt stator and ensure the long-term health of your Mercury outboard motor.

The history of Mercury 2-stroke outboard carburetors, specifically the transition between the WH, WMH, and WMV series, reflects the evolution of carburetion technology aimed at enhancing engine performance, efficiency, and reliability. 1. WH Series Carburetors: Introduction and Features: The WH series, introduced in the late 1970s and early 1980s, was known for its "Wide Horn" design, which allowed for greater air intake and improved fuel-air mixing. These carburetors were commonly used in high-performance and racing engines, particularly in Mercury's V6 models. The WH carburetors featured multiple venturis and larger throttle bores, enabling more precise fuel metering and higher power output. Applications: They were widely used in high-performance outboards such as the SST-140, SST-120, F1 / F200 tunnel boat and Pro Carb drag race classes, favored by enthusiasts and racers for their ability to provide a rich fuel mixture necessary for maximizing power. 2. WMH Series Carburetors: Development and Design Changes: The WMH series succeeded the WH series and was introduced in the late 1980s and early 1990s. This series featured a more compact design and refined 3-stage fuel metering systems. The WMH carburetors aimed to improve fuel efficiency and reduce emissions while maintaining performance. Technological Advancements: The WMH carburetors incorporated advances in carburetor technology, such as improved float and needle designs, which enhanced fuel flow control. They also featured better atomization of fuel, contributing to more efficient combustion. Usage: While orignal found on the the 2.5 Liter 150, 175, 200 and 245 HP outboards, they are still used in performance and drag race applications, the WMH series was also found in a broader range of outboard engines, including those designed for recreational use. 3. WMV Series Carburetors: Introduction and Characteristics: The WMV series represented further refinement in carburetor technology. Introduced in the mid-1990s, these carburetors focused on meeting stricter environmental regulations by reducing emissions and improving fuel economy. The WMV carburetors featured even more precise fuel metering and better control over air-fuel mixtures across different engine speeds and loads. Emission Standards and Efficiency: The development of the WMV series was driven by the need to comply with increasingly stringent emission standards. These carburetors were designed to optimize the air-fuel mixture for cleaner combustion, thus reducing pollutants like hydrocarbons and carbon monoxide. Wider Application: The WMV series was used across a range of Mercury 2-stroke outboards, including the SST-120, from small engines to larger 3.0 Liters, high-output models, reflecting a shift towards more environmentally friendly and fuel-efficient designs. Transition to Modern Fuel Systems: The introduction of electronic fuel injection (EFI) and direct fuel injection (DFI) systems marked the end of the carburetor era for Mercury's 2-stroke outboards. These systems offered superior fuel management, better performance, and significantly reduced emissions. EFI and DFI systems could precisely control the amount of fuel injected into the combustion chamber, leading to more efficient combustion and cleaner engine operation. Legacy: The WH, WMH, and WMV series carburetors represent significant milestones in the evolution of Mercury's 2-stroke outboard engines. Each series reflected the technological advancements and regulatory changes of its time, pushing the boundaries of performance and efficiency. Today, while these carburetors are largely replaced by more modern fuel injection systems, they are still valued by collectors and performance enthusiasts for not only their role in the history of marine engines but also the price point of building fast and reliable powerhead. Resources:

An outboard nose cone is a streamlined, hydrodynamic device that attaches to the front of the lower unit (gearcase) of an outboard motor. Its primary purpose is to provide a low water pick-up to reduce drag and improve the performance of the boat, especially at higher speeds. Here are some key points about outboard nose cones: Improved Hydrodynamics: The nose cone is designed to improve the water flow around the lower unit, reducing turbulence and drag. This helps the boat move more efficiently through the water. Higher Speed Stability: At higher speeds, the addition of a nose cone can improve the stability and handling of the boat. This is particularly beneficial for high-performance boats, such as racing boats or bass boats, where maintaining control at speed is crucial. Water Intake Location: Many nose cones are equipped with low water pickups, which allow the engine to be mounted higher on the transom without risking overheating. This is because the low water pickups are positioned to still draw water even when the lower unit is closer to the surface, which can be common in high-performance setups. Increased Propeller Efficiency: By streamlining the water flow, a nose cone can help reduce cavitation (when air bubbles form around the propeller blades) and improve the propeller's grip on the water, resulting in better thrust and fuel efficiency. Customization and Tuning: Nose cones are often used in conjunction with other performance modifications, such as propeller selection and engine height adjustments, to fine-tune the boat's performance for specific applications. Overall, an outboard nose cone is a useful upgrade for boaters looking to optimize their engine's performance and handling characteristics, particularly at high speeds.

For high-performance boating enthusiasts, finding the perfect destination means looking for the best water conditions, scenic beauty, and convenient boat launches, paired with excellent accommodations. Here’s a guide to ten of the top high-performance boating destinations in the USA, with everything you need to know for an unforgettable experience on and off the water. 1. Lake Havasu, Arizona Why It's Great:  Known as the "Hot Boat Capital of the World," Lake Havasu features warm waters, breathtaking desert landscapes, and hosts events like the Desert Storm Poker Run, drawing high-performance boaters from across the country. Boat Launches:  The Nautical Beachfront Resort offers a private boat launch ramp for hotel guests, providing easy and exclusive access to the lake. Accommodations:  The Nautical Beachfront Resort is a top choice, offering beachfront rooms, complimentary boat docks, and direct lake access, perfect for boaters looking for luxury and convenience. 2. Lake of the Ozarks, Missouri Why It's Great:  This large reservoir boasts winding waterways and hosts major boating events like the Lake of the Ozarks Shootout, one of the largest high-speed boat races in the country. Boat Launches:  Many resorts offer private boat ramps, such as Rippling Waters Resort, which features a concrete launch and covered docks. Accommodations:  Margaritaville Lake Resort offers a full-service marina, multiple dining options, and numerous recreational activities for a comprehensive getaway experience. 3. Key West, Florida Why It's Great:  Boating in Key West offers stunning ocean views, tropical weather, and numerous high-speed boating events, including the famous Key West Offshore World Championship. Boat Launches:  Garrison Bight Marina offers public boat ramps with easy access to the Atlantic Ocean. Accommodations:  The Perry Hotel & Marina Key West offers luxury accommodations and a full-service marina, ideal for boating enthusiasts. 4. Miami, Florida Why It's Great:  Miami offers a vibrant boating culture, turquoise waters, and direct ocean access, making it a prime spot for high-speed boating. The Miami Boat Show is a popular event drawing boaters from around the globe. Boat Launches:  The Matheson Hammock Park Marina features ramps providing convenient access to Biscayne Bay. Accommodations:  The Ritz-Carlton Key Biscayne offers luxurious lodging with easy access to the local boating scene. 5. Clear Lake, Texas Why It's Great:  This destination near Houston offers high-performance boaters access to both Clear Lake and nearby Galveston Bay, known for its smooth waters and ample space for speed enthusiasts. Boat Launches:  Clear Lake Park offers multiple ramps for boaters to easily access both Clear Lake and Galveston Bay. Accommodations:  South Shore Harbour Resort provides waterfront accommodations and convenient marina access for high-performance boating fans. 6. Chesapeake Bay, Maryland/Virginia Why It's Great:  The Chesapeake Bay offers expansive waters, charming coastal towns, and a strong boating community, perfect for fast-paced boating and leisurely cruising alike. Boat Launches:  Sandy Point State Park features public ramps with direct access to the bay. Accommodations:  The Inn at Perry Cabin offers upscale lodging and marina services, ensuring comfort after a day on the water. 7. Lake Cumberland, Kentucky Why It's Great:  Lake Cumberland is known for its deep water and scenic surroundings, hosting events like the Thunder Run, which draw high-speed boating enthusiasts every year. Boat Launches:  Lake Cumberland State Resort Park offers several boat ramps for easy access to the lake. Accommodations:  The Lake Cumberland State Resort Park offers lodge rooms, cabins, and spectacular views of the water. 8. Lake Michigan (Chicago, Illinois) Why It's Great:  Boating along Chicago’s Lake Michigan shoreline provides a thrilling urban backdrop with wide-open waters ideal for high-speed adventures, coupled with views of the iconic Chicago skyline. Boat Launches:  The 31st Street Harbor features ramps that provide access to Lake Michigan. Accommodations:  The Langham, Chicago offers luxury lodging near the lakefront, combining urban luxury with proximity to Lake Michigan’s boating opportunities. 9. Lake Erie Islands, Ohio Why It's Great:  With islands like Put-In-Bay, this destination offers clear waters, great beaches, and a vibrant boating atmosphere, perfect for high-speed boating enthusiasts. Boat Launches:  Catawba Island State Park has public ramps for easy access to Lake Erie and its islands. Accommodations:  The Put-in-Bay Resort & Conference Center is a prime spot, offering comfortable lodging and close proximity to marinas. 10. Mississippi River (Various Locations) Why It's Great:  Popular for poker runs and speed events, the Mississippi River offers long stretches of navigable waters, winding through diverse scenery ideal for boating adventures. Boat Launches:  The Port of Dubuque Marina in Iowa features ramps with access to the Mississippi River. Accommodations:  Hotel Julien Dubuque provides comfortable and stylish accommodations near the riverfront, perfect for winding down after a day on the water. Each of these destinations offers high-performance boating enthusiasts the ideal mix of thrilling waters, convenient boat launches, and excellent accommodations to make for a memorable trip. Whether cruising across the wide waters of Lake Michigan or exploring the tropical beauty of Key West, these spots guarantee a fantastic boating experience. Let us know what we missed in the comments.

Numbered drill bit sizes range from 80 (smallest) to 1 (largest). The numbers on numbered drill bits relate to wire gauges, so larger numbers indicate smaller drills. Mercury 2-stroke outboard carb jet sizes, on the other hand, are related to thousandths of an inch which matches typical jet sizes found in both main and air jets in WH, WMV, WMH, and other carburetor types. A jet size primary passage bore in diameter indicates flow rate. Larger main jets (which carry fuel) are "fatter", while, larger air jets (which carry air) make those circuits "leaner". While jets should be reamed or bored (not drilled) to ensure a consistent diameter, drilling jets can be an affordable way to make bigger jets to save or tune a motor that is too lean. This numbered drill bit chart is correlated with typical outboard carburetor jet sizes. Numbered drill bit kits can be purchased at your favorite tool stores. We've created this chart as a convenient reference with the most common numbered drill bits sizes (39 to 59) used to enlarge more common smaller jets to larger sizes when otherwise not available to purchase. To drill a jet with numbered drill bits, you can try these steps: Run the engine with the stock main jet, and determine if too lean If lean, use a drill bit that's one size larger to drill out the jet Run the engine again and take another read Repeat until jetted properly Below is a free printable cheat sheet included in our Carburetor Jet Number Drill Bit Kits!

The Yamato 302 is a racing outboard motor designed for the UIM outboard series OSY 400. Model 302 is a 24.2 cubic inch stock racing engine. Like its predecessors, this motor was developed specifically for use: in the multi-billion dollar pari-mutuel boat racing industry in Japan. The motors are first raced in stadiums in Japan and then rebuilt and inspected in the factory before being delivered to APBA and UIM circuit racers. These motors are required to run heat after heat, day after day with perfect reliability at racing speeds. Download the Yamato Service & Technical Manual in PDF

For high-performance 2-stroke outboard enthusiasts, fine-tuning every detail of an outboard engine can be the difference between winning and losing or running well and not running. One of the most crucial tuning elements is setting your maximum ignition timing advance. Ignition timing dictates when the spark plug fires relative to the piston’s position in the cylinder, impacting power, efficiency, and engine longevity. This guide, paired with an easy-to-use HTML timing calculator, will help boat owners and racers achieve optimal ignition timing for their 2-stroke Mercury V6 and OMC V6/V8 outboards. Why Proper Maximum Timing Advance Matters Ignition timing plays a major role in your engine’s performance, fuel efficiency, and reliability. Incorrect timing can lead to serious engine problems like pre-ignition, detonation, or even catastrophic damage. Understanding how to set and analyze ignition timing is essential for maximizing performance while maintaining engine health. How to Leverage this Guidance Tool Our interactive HTML tool lets you adjust max timing advance by selecting a value between 0° and 40° BTDC (Before Top Dead Center) with a slider. The tool displays real-time feedback on the engine’s potential behavior based on the chosen timing. Here’s the general guidance for each max timing range: - **0° to 4° BTDC**: Timing is extremely retarded, leading to severe power loss, rough idling, and inefficient combustion. - **5° to 10° BTDC**: Timing is still retarded, resulting in reduced power and possible misfires. - **11° to 12° BTDC**: The engine runs, but power and fuel economy are below optimal levels. - **13° to 16° BTDC**: Suitable for some OMC V6 or V8 models, but not ideal for peak performance in Mercury V6s. - **17° to 19° BTDC**: Too low of a range for optimal Mercury V6s performance; Way too high for most OMC V6 and V8 models. - **20° to 22° BTDC**: Safe advance with a good range of performing for most Mercury V6s; 2.0, 2.4, and 2.5 Liters. - **23° to 25° BTDC**: Slightly advanced, providing more power but starting to increase the stress on engine parts. Premium pump gas is recommended. - **26° to 27° BTDC**: Highly advanced, delivering noticeable power gains but with high risk of pre-ignition and component stress. Use higher-octane race fuel and a richer mixture. - **28° to 30° BTDC**: Extremely advanced, offering significant power up to 6,500 RPM, but performance drops above 7,000 RPM. Reserved for short drag races with high-octane fuel and enriched mixtures. - **31° BTDC and above**: Excessively advanced and dangerous, risking severe detonation and catastrophic engine failure—proceed at your own peril. Practical Tips for Everyday Boaters and High-Performance Users Understanding these timing ranges is essential for racers and performance enthusiasts looking to push their engines to the limit. For recreational boaters, Mercury V6s often perform best between 20° and 22° BTDC, while the OMC V6 and V8 should be between to 12° and 14°. For River Racers, Mercury V6s often perform best between 24° and 25° BTDC, while the OMC V6 and V8 should be around 14°. For Circuit and Circle Boat Racer, Mercury V6s often perform best between 25° and 27° BTDC, while the OMC V6 and V8 should be around 14° to 16°. For Outboard Drag Racers, the Mercury V6 can run 28° to 30° BTDC full advance for 660 to 800 feet, and while fully aware of the need for specialized fuel and close monitoring, while the OMC V6 and V8 could creep up to 16°. Why Bother with More Timing Advance Advancing ignition timing before top dead center (BTDC) in a 2-stroke outboard engine increases horsepower by optimizing combustion. Igniting the fuel-air mixture earlier allows peak cylinder pressure to occur right around or just after TDC, ensuring the maximum force pushes the piston down during the power stroke. This timing improves energy transfer and torque, boosting power output. Earlier ignition in the upward piston stroke gives more time for the fuel to burn completely. At higher RPMs, pistons move quickly, and advanced timing compensates for the reduced combustion window, maintaining efficient power generation. The result is higher cylinder pressure at the optimal moment, which maximizes power extraction from the expanding gases. However, advancing timing too much can lead to pre-ignition and detonation, causing severe damage due to uncontrolled pressure and heat. The engine will also start to "fight against it's momentum" as the RPMs exceed a certain point. Key Points to Remember **Prioritize Safety**: Advanced timing can deliver impressive power but comes with higher risks. **Choose the Right Fuel**: High-octane race fuel and richer mixtures are crucial for advanced timing settings to prevent engine detonates. **Monitor Your Engine**: Use real-time feedback and diagnostic tools to ensure safe operation and avoid long-term damage. By using this timing tool and understanding what each setting means, you can optimize your 2-stroke outboard’s performance and maintain engine health. Whether you’re a racer or a performance enthusiast, finding the balance between power and reliability is key to staying ahead of the competition.

This is a free online resource to find mostly out-of-production, no longer available Mercury Racing Owners Manuals with specifications for V6 2-stroke outboards and a few currently produced 4-stroke outboard models. All are in PDF files making them available for online download to your desktop computer, laptop, or as a file to your mobile phone. Once downloaded, PDF files can be printed for your use. 2-Stroke Owners Manuals with Specs Mercury Racing 3.0 Liter 300X Pro Max w/ Sportmaster Manual - Free The below service manuals are available for purchase:

This is a free online resource to find mostly out-of-production, no longer available Mercury Racing Owners Manuals with specifications for V6 2-stroke outboards and a few currently produced 4-stroke outboard models. All are in PDF files making them available for online download to your desktop computer, laptop, or as a file to your mobile phone. Once downloaded, PDF files can be printed for your use. 2-Stroke Owners Manuals with Specs Mariner 2.5 Liter Super Magnum 200 and 225 HP Manual - Free The below service manuals are available for purchase:

This is a free online resource to find mostly out-of-production, no longer available Mercury Racing Owners Manuals with specifications for V6 2-stroke outboards and a few currently produced 4-stroke outboard models. All are in PDF files making them available for online download to your desktop computer, laptop, or as a file to your mobile phone. Once downloaded, PDF files can be printed for your use. 2-Stroke Owners Manuals with Specs Mercury Racing 260 HP ROS (2.5 Liter EFI) Manual - Free These are available for purchase:

This is a free online resource to find mostly out-of-production, no longer available Mercury Racing Owners Manuals with specifications for V6 2-stroke outboards and a few currently produced 4-stroke outboard models. All are in PDF files making them available for online download to your desktop computer, laptop, or as a file to your mobile phone. Once downloaded, PDF files can be printed for your use. 2-Stroke Owners Manuals with Specs Mercury Racing 2.5 Liter S3000 / F1 w/ Superspeed Master (SSM) #4 Owners Manual - Free Below are available for purchase: