Gordon Jennings' Two-Stroke Tuners Handbook  holds particular significance for outboard engine builders due to its detailed exploration of two-stroke engine tuning principles, many of which are directly applicable to optimizing outboard motors. Here’s why it’s important: Optimization of Performance : Outboard engines, especially those used in racing or high-performance applications, benefit greatly from the tuning techniques outlined in Jennings' handbook. Builders can apply his methods to improve power output, efficiency, and overall performance of two-stroke outboards. Porting and Cylinder Design : Jennings delves into the intricacies of port timing and cylinder head modifications, both of which are critical in maximizing the performance of two-stroke outboard engines. Builders can use this knowledge to fine-tune the engine's powerband, making it more suitable for specific marine applications. Exhaust System Tuning : The book provides a thorough analysis of expansion chambers and exhaust tuning, which are crucial for outboard engines that rely heavily on proper exhaust flow for performance. Jennings' insights help builders design or modify exhaust systems to achieve the desired power characteristics. Fuel and Carburetion Tuning : Outboard engines often operate in varying conditions, from idle to full throttle. Jennings’ guidance on carburetion and fuel tuning helps builders ensure that the engine runs optimally across all these conditions, enhancing reliability and performance on the water. Ignition Timing and Engine Reliability : Proper ignition timing is vital for the longevity and efficiency of outboard engines. Jennings’ handbook offers a detailed understanding of ignition dynamics, which builders can use to set up the engine for maximum performance without compromising reliability. Adaptability to Marine Environments : Although the book primarily focuses on land-based engines like motorcycles, the principles are adaptable to marine engines. Builders can translate the tuning techniques to address the specific challenges of operating in a marine environment, such as cooling and corrosion. Legacy and Knowledge Base : For many outboard engine builders, Jennings' book is a cornerstone of their technical library. It has inspired a deeper understanding of two-stroke engine dynamics, leading to innovations and improvements in outboard engine design and tuning over the years. Overall, Gordon Jennings' Two-Stroke Tuners Handbook  serves as a crucial resource for outboard engine builders seeking to enhance the performance, reliability, and efficiency of two-stroke outboard motors. Download the PDF of the original 1973 Two-Stroke Tuners Handbook by Gordon Jennings, Online for Free.

When using a digital inclinometer to measure the pitch of a boat propeller, the "Blade Angle × Constant" method is a straightforward approach used by the Buckshot Racing #77 Formula 1 Tunnel Boat Racing Team. The constant is typically related to the propeller's diameter and the point at which the measurement is taken, which in this case is at 75% of the radius. We've included a proprietary Buckshot Racing #77 Calculator Sheet to make these instructions below much simpler, but included the detail for those who want to take a deeper dive into the math. Tools You'll Need: Digital inclinometer Ruler or tape measure Calculator (Print the Buckshot Racing #77 Calculator Sheet) Steps to Calculate Pitch Using Blade Angle × Constant: Position the Propeller: Place the propeller on a flat, stable surface. Set the Measurement Point: Identify the point that is 75% of the way from the hub to the tip of the blade. This is done by measuring the propeller's radius (half of the diameter). For example, if the propeller diameter is 14 inches, the radius is 7 inches. 75% of this radius is 0.75 × 7 = 5.25 inches. Mark this point on the blade. Measure the Blade Angle: Place the digital inclinometer flat against the blade at the 75% radius mark. Read and record the blade angle shown on the digital inclinometer. Determine the Constant: The constant is derived from the diameter and the position at which the angle is measured. For simplicity, the constant can be approximated as: Constant=Propeller Diameter×π360∘\text{Constant} = \frac{\text{Propeller Diameter} \times \pi}{360^\circ} Constant=360∘Propeller Diameter×π​ This accounts for the propeller’s diameter and translates the angle into a linear distance. Calculate the Pitch: Use the formula: Pitch=Blade Angle×Constant\text{Pitch} = \text{Blade Angle} \times \text{Constant}Pitch=Blade Angle×Constant Substitute the angle and constant into the formula to calculate the pitch. Example Calculation: Propeller Diameter:  14 inches 75% of Radius:  5.25 inches Measured Blade Angle:  20 degrees Calculate the Constant: Constant=14×3.1416360=0.1223 inches per degree\text{Constant} = \frac{14 \times 3.1416}{360} = 0.1223 \text{ inches per degree}Constant=36014×3.1416​=0.1223 inches per degree Calculate the Pitch: Pitch=20∘×0.1223=2.446 inches\text{Pitch} = 20^\circ \times 0.1223 = 2.446 \text{ inches}Pitch=20∘×0.1223=2.446 inches The pitch of the propeller, based on these calculations, would be approximately 2.446 inches per revolution. Notes: Calibration:  Ensure that the inclinometer is properly zeroed before measuring. Average of Multiple Blades:  For accuracy, measure the blade angle at the same point on each blade and take the average. Blade Variations:  Account for any variations in the blade angles by averaging them if necessary. This method provides a simplified yet effective way to calculate the propeller pitch using a digital inclinometer. Download our Free how-to-measure-prop-pitch-calculator-sheet, kindly reference Buckshot Racing #77 when sharing.

While electronic fuel injection (EFI) systems often provide better performance, there are still several advantages to run WH, WMH, WMV carburetors on a Mercury 2.0, 2.4, or 2.5 Liter 2-stroke outboard: 1. Simplicity: Carburetors are mechanically simpler than EFI systems, making them easier to understand, maintain, and repair. This simplicity can be advantageous for users who prefer straightforward mechanical systems. 2. Cost: Carburetors are less expensive than Mercury and aftermarket EFI systems, both in terms of initial purchase and potential repair costs. This makes them a more budget-friendly option. 3. Ease of Repair: Carburetors can often be repaired with basic tools and mechanical knowledge, whereas EFI systems may require specialized diagnostic equipment and expertise. 4. Fewer Electronics: Carburetors do not rely on electronic components, which can be a benefit in harsh marine environments where electronics might be prone to corrosion or failure. 5. Tuning Flexibility: For enthusiasts and boat racers, carburetors offer more hands-on tuning options. Adjustments to the air-fuel mixture and other parameters can be made manually, allowing for customized performance settings. 6. Compatibility: Carburetors can be more compatible with older or simpler outboard engine setups that may not support the electronic control systems required for EFI. While EFI systems generally provide better performance and efficiency, carburetors still offer a range of practical advantages that can make them a preferred choice in certain situations.

In Gordon Jennings' 1978 article in Cycle Magazine on two-stroke oil premix, he observed that using a higher ratio of two-stroke oil in the fuel mixture (meaning more oil relative to fuel) did indeed result in increased horsepower. This finding was somewhat counterintuitive because conventional wisdom suggested that more oil could potentially dilute the fuel mixture and reduce power output. Jennings' conclusion was based on the understanding that the additional oil provided better sealing of the piston rings and improved lubrication, reducing friction and enhancing the combustion process. This improved sealing led to better compression and more efficient combustion, ultimately increasing the engine's power output. The article delves into the following key aspects: Lubrication Needs: Jennings explains that two-stroke engines rely on the premixed oil to lubricate their internal components, as these engines lack a separate lubrication system. Importance of Oil-to-Fuel Ratios: The correct oil-to-fuel ratio is crucial for engine performance and longevity. Jennings discusses how different engines and conditions require different ratios, commonly ranging from 15:1 to 50:1. Oil Types: The article examines various oil types, such as mineral-based and synthetic oils, and stresses the importance of choosing the appropriate oil based on the engine's requirements and operating conditions. Fuel Quality: Jennings emphasizes the significance of using high-quality fuel to avoid engine issues like poor performance and increased wear. Mixing Techniques: Proper mixing techniques are highlighted to ensure an even distribution of oil in the fuel. Jennings advises thoroughly shaking the fuel container and mixing smaller quantities if the engine isn't used frequently. Common Issues and Solutions: The article addresses problems like oil separation, excessive smoke, and carbon buildup. Jennings suggests adjusting the oil ratio and using high-quality oils to mitigate these issues. However, it's important to note that while higher oil ratios can increase horsepower, they also result in more smoke and potential carbon buildup, so the optimal ratio needs to balance power output with engine longevity and cleanliness. You can download the full copy of Gordon Jennings' 1978 article on two-stroke oil premix here:

Outboard engine manufacturers often use roller bearings instead of friction bearings (such as plain bearings or bushings) in 2-stroke engines for several reasons: Load Handling Capability: Roller bearings, particularly needle roller bearings, can handle higher radial and axial loads compared to friction bearings. This is important in outboard engines where the crankshaft experiences varying and sometimes significant loads due to the nature of marine propulsion. Durability and Reliability: Roller bearings are generally more durable and have a longer service life than friction bearings. They are designed to withstand higher stresses and provide consistent performance over extended periods, which is crucial for the reliability of outboard engines operating in harsh marine environments. Reduced Friction and Heat Generation: Roller bearings typically exhibit lower friction compared to friction bearings, which reduces energy loss and heat generation. In a 2-stroke outboard engine, minimizing friction helps optimize fuel efficiency and overall performance. Compact Design: Roller bearings can often be designed to have a more compact profile compared to friction bearings of similar load capacity. This compactness is beneficial for packaging within the constrained spaces of outboard engines. Maintenance Considerations: Roller bearings generally require less maintenance compared to friction bearings. They are less susceptible to wear and typically do not require lubrication or replacement as frequently, reducing downtime and maintenance costs for outboard engine operators. Industry Standard: Roller bearings have become a standard choice in modern outboard engine designs due to their proven performance and reliability. They are well-suited to handle the operational demands and stresses encountered in marine applications. Overall, the use of roller bearings in 2-stroke outboard engines is driven by their superior load handling capabilities, durability, reduced friction, and suitability for marine environments. These factors collectively contribute to improved performance, efficiency, and reliability of outboard engines. *Picture here is the original patent for the Upper Main Bearing found in the Mercury 2.4 Liter 2-Stroke V6 Outboards with 1 3/8" top journal on the crank. AKA the OEM part number 93496, 31-93496T or RBC TJ-75117-11 filed under Patent 3382016 "Arrangement of tandem rollers in a roller bearing and method of assembling same". This bearing was designed to handle 8,500 RPMs and was selected for the motor based on: Load Distribution: Tandem roller bearings are designed to handle heavy radial and axial loads simultaneously. They distribute the load across a larger surface area compared to single-row bearings, which can improve bearing life and performance. High Load Capacity: They are capable of supporting higher radial and axial loads, making them suitable for applications where significant forces are acting in multiple directions. Reliability: These bearings have been used for many years in various industrial applications, indicating their reliability and established performance in demanding conditions.

Here are the standard Factory Carb Jet Sizes for Mercury Racing 2.4 Liter Bridgeport, 2.4 Liter MOD VP, and 2.0 Liter XR2. This Jetting Chart includes the Mains and Idles that were found in the WH46 and WH48 Carburetors.

Tuning a 2-stroke outboard engine for high performance requires expertise and careful adjustments due to its specialized nature. Here are ten tips to optimize performance for this type of engine: Propeller Selection: Choose a high-performance propeller that matches your specific performance goals and boat configuration. Consider factors such as diameter, pitch, and material to maximize acceleration, top speed, and handling. Fuel Quality and System: Use high-octane fuel to prevent detonation and optimize performance. Ensure the fuel system is clean and free of contaminants. Consider upgrading to a high-flow fuel pump and using larger fuel lines to meet the engine's demands at high speeds. Carburetor or Fuel Injection Tuning: Fine-tune the carburetor or fuel injection system to optimize air-fuel mixture throughout the RPM range. Adjust idle mixture, mid-range response, and wide-open throttle settings for peak performance without sacrificing reliability. Ignition System: Upgrade to a high-performance ignition system with programmable features if possible. Optimize ignition timing and spark advance curves for maximum power output and efficiency across different RPM ranges. Exhaust Tuner: The right exhaust tuner size, shape, and length can improve scavenging, reduce back pressure, and enhance overall engine performance and responsiveness. Cooling System: Ensure the engine cooling system is efficient and capable of handling high-performance demands. Monitor engine temperatures closely and consider upgrades like high-flow water pump kits or improved cooling passages to prevent overheating. Porting and Polishing: Consider professional porting and polishing of intake and exhaust ports to improve airflow efficiency. This can significantly increase power output, especially at higher RPMs. Work with experienced tuners who understand the nuances of porting for high-performance marine engines. Compression and Cylinder Head Optimization: Regularly check and maintain optimal compression levels across all cylinders. Ensure cylinder heads are properly machined and sealed to prevent leaks and maximize combustion efficiency. Propeller Shaft Height and Trim Optimization: Adjust the propeller shaft height and trim settings to optimize performance and efficiency. Experiment with different settings to find the ideal balance for acceleration, top speed, and fuel economy based on your boat's hull design and conditions. Regular Maintenance and Monitoring: Maintain the engine meticulously by following recommended service intervals and performing regular inspections. Monitor spark plug condition, fuel system integrity, and overall engine health to ensure consistently high performance and reliability. It's crucial to approach tuning with care and attention to detail, especially with high-performance 2-stroke outboards. Consider consulting with experienced tuners or marine mechanics who have specific expertise with these engines to achieve the best results while maintaining reliability and longevity.

The Buckshot Racing #77 Mercury V6 Oil Injection Block-Off Kit is designed for Mercury 2.0 Liter, 2.4 Liter, and 2.5 Liter two-stroke V6 outboards being converted from factory oil injection to premixed fuel. This kit is commonly used by racers, engine builders, tuners, and performance boat owners who want to eliminate the original mechanical oil injection pump system and run a controlled fuel-and-oil premix. Many high-performance Mercury V6 owners choose premix when building modified, high-RPM, or race-use engines because premix removes the dependency on aging oil injection parts, oil hoses, pump drive components, warning modules, check valves, and remote oil tank hardware. This is especially common on performance Mercury 2.4L and 2.5L engines that see elevated RPM, aggressive acceleration, surfacing propeller use, or race-duty operation. This oil injection block-off kit is compatible with Mercury-style applications using part numbers 818304A1, 8M0095447, 43453, 43453T, and 32509. It is intended for Mercury V6 two-stroke outboards where the oil injection pump is being removed and the engine will be operated on properly mixed premix fuel. What the Oil Injection Block-Off Kit Does The factory Mercury oil injection system uses a crankcase-driven oil pump to meter oil into the fuel system. When converting to premix, the oil pump is removed and the opening in the crankcase must be sealed properly. The Buckshot Racing #77 block-off kit replaces the removed oil pump assembly with a block-off plug, O-ring, and mounting hardware to seal the oil pump cavity. A proper block-off installation prevents crankcase air leaks, oil seepage, and contamination while allowing the engine to operate on premixed fuel. Because two-stroke engines rely on oil in the fuel for internal lubrication, the engine must never be run on straight gasoline after the oil injection system is removed. Why Racers and Builders Convert to Premix Premix is popular in Mercury performance builds because it gives the owner direct control over the fuel-to-oil ratio. Instead of relying on an older mechanical oiling system, the operator mixes the correct amount of two-stroke oil directly into the fuel tank before running the engine. This simplifies the engine, removes several potential failure points, and makes the fuel system easier to inspect and service. The tradeoff is responsibility. Once the oil injection system is removed, every gallon of fuel must be mixed correctly. If the boat is filled with straight gas by mistake, the engine can suffer rapid bearing, piston, ring, and cylinder damage. Installation Overview Begin by disconnecting the battery and making sure the engine is cool. Work in a clean, well-ventilated area and keep dirt out of the intake, crankcase, fuel system, and oil passages. Drain or remove oil from the remote tank, engine-mounted oil tank, oil hoses, and pump area to prevent spills. Remove the cowling and any components blocking access to the oil injection pump. Carefully disconnect the oil lines from the pump and cap or remove unused lines so they cannot leak, drip, or allow contamination into the engine area. Unbolt the oil pump from the crankcase and remove the pump, O-ring, long drive shaft, sleeve, and related oil injection hardware as required for your specific Mercury V6 configuration. Clean the oil pump mounting surface thoroughly. The sealing area must be free from old gasket material, oil residue, corrosion, and debris. Install the Buckshot Racing #77 block-off plug with the supplied O-ring and mounting screws. Use only a light film of appropriate marine sealant if needed around the o-ring sealing area. Do not overuse sealant, and do not allow sealant to enter the crankcase. Tighten the supplied screws evenly and carefully. The block-off cap should be secure, but over-tightening can damage the cap, threads, or sealing surface. Reinstall any removed components and inspect the area for proper clearance, clean routing, and secure hardware. Premix Fuel Requirements After installation, drain any unmixed fuel or clearly confirm the fuel in the tank is properly mixed before starting the engine. The correct fuel-to-oil ratio depends on the engine build, oil type, break-in status, operating RPM, and Mercury or engine builder recommendation. Many Mercury V6 premix applications use ratios in the 24:1 to 50:1 range depending on use. Fresh rebuilds, race engines, and break-in procedures may require a richer oil mixture than normal recreational use. Always mix fuel and oil thoroughly before running the engine. Use high-quality marine two-stroke oil appropriate for your Mercury V6 outboard and never assume the tank is mixed unless you personally verified it. Warning System and Alarm Notes Removing the oil injection system changes the warning system. The factory oil warning circuit and oil injection alarm will no longer function as originally designed once the oil injection pump and related components are removed. However, the over-temperature alarm should remain functional. On many Mercury V6 warning systems, the overheat alarm circuit uses the tan/blue wire. With the key on, grounding the tan/blue temperature warning lead should activate the warning horn. This test helps confirm that the over-temperature alarm circuit still works after the oil injection conversion. If you are unsure how your warning system is wired, consult the correct Mercury service manual or have the system checked by a qualified marine technician. The oil injection warning module may be removed or disconnected during conversion, depending on the engine setup. Any unused wiring should be insulated, secured, and protected from short circuits. Do not remove or disable the over-temperature warning circuit. Crankshaft Gear and Internal Volume Note On Mercury V6 oil injection conversions, many builders leave the crankshaft oil pump drive gear in place unless the engine is being fully disassembled and properly reconfigured. Removing internal components without understanding the crankcase volume and airflow effects can change how that cylinder behaves. If the powerhead is apart and the gear is being removed, the work should be handled by an experienced Mercury V6 builder. Label the Boat Clearly After converting to premix, label the boat clearly so no one accidentally adds straight gasoline. Place visible “PREMIX ONLY” labels near the fuel fill, fuel tank, dash, and engine rigging area. This is one of the most important steps in the conversion because one fueling mistake can destroy a two-stroke powerhead. Final Startup and Inspection Before starting the engine, verify that the block-off plug is sealed, all unused oil hoses are removed or capped, all wiring is secured, the battery is reconnected, and the fuel tank contains the correct premix. Start the engine on a proper water supply and let it idle briefly while inspecting the block-off area for leaks or air intrusion. Confirm stable idle, normal water flow, and proper warning horn function before running the boat. After the first run, remove the cowling and inspect the block-off plug, fasteners, fuel system, and wiring again. On performance engines, continue monitoring plug color, piston wash, temperature, water pressure, and fuel quality as part of normal tuning. Buckshot Racing #77 Note: The Buckshot Racing #77 Mercury V6 Oil Injection Block-Off Kit is a practical upgrade for Mercury 2.0L, 2.4L, and 2.5L two-stroke outboards being converted to premix fuel. Compatible with Mercury-style part numbers 818304A1, 8M0095447, 43453, 43453T, and 32509, this kit gives racers, builders, and performance boat owners a clean way to remove the factory oil injection pump and seal the crankcase properly. For Mercury V6 race engines, lake motors, drag boats, tunnel hulls, and high-performance outboard builds, a properly installed oil injection block-off kit helps simplify the engine, improve serviceability, and support reliable premix operation when fuel is mixed correctly every time.

Nikasil® is a common term used to describe a cylinder bore that has been plated with nickel silicon carbide, and then finished to a precise bore diameter and very specific finish. Silicon carbide is an extremely hard ceramic material and requires a honing process using diamond hone tooling. Due to this extremely hard surface, the cylinder wall will have very strong wear properties over time. In Mercury Racing outboard engines, Nikasil sleeves are often used to line the cylinders in the 245 HP Carb, 260 EFI, 280 ROS, and 300 Drag. This coating is known for its hardness and wear resistance, which helps to maintain cylinder shape and prevent excessive wear, even under high-performance conditions. It's a popular choice in high-performance engines like those used in racing or high-speed boating applications because it can withstand the stresses and heat generated by these engines better than traditional cylinder materials. Under normal use from combustion, there will be a buildup of carbon and burnt oil on the bore surface known as “glaze”. Glaze will prevent the rings from properly seating during the break-in process, therefore it needs to be removed.

Identifying bad gas in a two-stroke outboard can be crucial for maintaining performance and preventing damage. Here are some signs that you might have bad gas in your engine: 1. Hard Starting: Difficulty starting the engine or needing multiple attempts to get it running can indicate bad gas. 2. Rough Idling: If the engine runs unevenly or stumbles at idle, this could be a sign of fuel issues. 3. Reduced Power: A noticeable drop in performance, such as lower speed or power output, might suggest the fuel is no longer providing optimal combustion. 4. Engine Misfires: Irregular or inconsistent firing of the engine, often accompanied by unusual noises, can be caused by degraded fuel. 5. Poor Acceleration: If the engine hesitates, sputters, or fails to respond smoothly when you accelerate, bad gas could be the culprit. 6. Increased Smoke: Excessive smoke from the exhaust can indicate improper combustion, often due to bad or old fuel. 7. Fuel Odor: Bad gas often has a sour or varnish-like smell, different from the normal gasoline odor. 8. Clogged Carburetor/Fuel Injectors: Residues and varnish from old gas can clog the carburetor or fuel injectors, leading to poor engine performance. To confirm if bad gas is the issue, you can: Inspect the Fuel: Check the fuel for discoloration or debris. Good gasoline should be clear and free from particles. Smell the Fuel: Fresh gasoline has a specific, sharp odor. If the gas smells sour or like varnish, it’s likely gone bad. - Test with Fresh Fuel: If you suspect bad gas, drain the fuel tank and replace it with fresh gasoline. If the engine runs better with the new fuel, it confirms the old gas was problematic. Regular maintenance and using fresh, high-quality fuel can help prevent these issues and keep your two-stroke racing outboard performing at its best.

Find custom Mercury driveshafts and driveline components for 2.0L, 2.4L, and 2.5L V6 outboards. Built for performance and accuracy, our parts ensure proper fitment for short shaft, offshore, and racing setups. When working on Mercury Marine and Mercury Racing V6 outboards, correctly measuring the driveshaft length is essential for proper fitment, alignment, and performance. Whether you are rebuilding a lower unit, swapping midsections, or ordering a custom driveshaft from Buckshot Racing #77, accuracy matters. This applies across all Mercury 2.0L, 2.4L, and 2.5L V6 platforms, including popular engines such as the 150, 175, 200, 225 Pro Max, XR2, XR4, XR6, XRi, 260 EFI, 280 ROS, and 300 Drag. When 15" Isn’t 15" 🤔 One of the most common misconceptions is assuming that a “15-inch midsection” equals a 15-inch driveshaft. The same misunderstanding applies to 20-inch and 25-inch mids. In reality, the advertised midsection length does not reflect the actual driveshaft measurement. Mercury’s design includes additional internal stack height between the crankshaft, midsection, and gearcase. Because of this, the driveshaft is always longer than the nominal midsection length. The Correct Way to Measure a Mercury Driveshaft ⚖️ The only accurate way to measure a Mercury driveshaft is by measuring from the very tip of the driveshaft (top spline) down to the gearcase mounting surface, which is where the lower unit bolts to the midsection. This “tip-to-mounting-surface” measurement is the industry standard and is what should always be used when identifying or ordering a driveshaft. The Simple Rule: “Measure and Subtract 3” 🤓 A helpful rule used throughout the marine industry is to measure the driveshaft and subtract approximately three inches to determine the midsection length. For example, a driveshaft that measures ~18 inches from tip to mounting surface corresponds to a 15-inch midsection. A ~23-inch measurement aligns with a 20-inch mid, and a ~28-inch measurement matches a 25-inch midsection. This rule works because Mercury’s design consistently adds roughly three inches between the nominal mid-length and the actual driveshaft length. Why Accuracy Matters Using the wrong driveshaft length can lead to serious mechanical issues. If the shaft is too short, it may not fully engage the crankshaft splines, which can cause stripping or failure under load. If it is too long, it can create binding, improper seating, or damage to internal components. In high-performance engines like the 260 EFI, 280 ROS, and 300 Drag, precision becomes even more critical. These engines operate at higher RPM and load levels, where even small misalignments can lead to premature wear or catastrophic failure. Consistency Across Mercury V6 Platforms Mercury maintained a consistent driveshaft design across its 2.0L, 2.4L, and 2.5L V6 two-stroke outboards, which is why this measurement method applies broadly. Whether working on a 150 HP fishing motor, an XR6 lake setup, or a 280 ROS race engine, the same principles apply. This consistency makes it easier to identify, measure, and replace driveshafts across a wide range of Mercury applications. Custom Driveshafts from Buckshot Racing #77 At Buckshot Racing #77, we offer brand-new Mercury driveshafts available in custom lengths to support everything from stock rebuilds to full performance conversions. If you are running a short shaft setup, offshore mid, or custom race configuration, we can supply a driveshaft built to your exact tip-to-mount measurement, ensuring proper fit and performance. Final Takeaway The most important concept to remember is simple but critical. Always measure from the tip of the driveshaft to the mounting surface, and then subtract approximately three inches to determine the corresponding midsection length. Because in the world of Mercury outboards, 15 inches doesn’t actually mean 15 inches—and getting that detail right makes all the difference. For technical support or custom orders, contact Buckshot Racing #77, your trusted source for Mercury performance parts and driveline solutions.

“Rooster Tail” is a jet stream of water that shoots into the air behind a boat. It’s created when the propeller tilts back and shoots an amazing display of water resembling an outstretched rooster’s tail. Although impressive, high rooster tails can indicate that the boat is over-trimmed or that the bow is dropping and the boat is losing performance. “Prop Slip” is the difference between the theoretical and actual forward speed of a boat based on the angle of the blades. The propeller naturally “slips” and doesn't travel the full distance in one revolution. Propeller slip is not a steady factor and is constantly changing. It accounts for efficiency loss due to weight, drag, hydrodynamics, and aerodynamics. But it’s not an absolute determining factor, typically there is a range of preferred slip percentages to find your optimal propeller based on your boat, motor, set-up, and performance objectives. “On the Drain Plug” is a saying that the boat is flying well, just almost none of the hull dragging or the boat is riding just on the drain plug. Boaters are reminded to pull the drain plug as a boat leaves a ramp to avoid spreading unwanted plants or animals to other water bodies. It is also illegal in some places to have your drain plug installed with your boat trailered on public roads. “When in Doubt, Trim it Out” means to raise the bow of a boat slightly. Trim is the running angle of the boat in the water. When you adjust the outboard’s trim, you can raise or lower the bow. When finding the optimal trim, you can improve the boat's performance and fuel economy, too much (blowover) or too little (hook) might cause a catastrophic wreck. “Prop It” often refers to trying different propellers to see how they perform. The propeller's size and type are put on the boat, and the boat is test-run at wide-open throttle. The propeller's pitch and size can cause the boat to be over-propped or under-propped. Over-propped means the engine cannot achieve its max-rated RPM. Under-propped means the engine reaches max RPM too easily, so the boat doesn't go as fast as expected. “Setback” in outboard boating is the distance between the transom plus jack plate to the trailing edge of the running surface of the hull. The more setbacks, the more leverage the motor has on the boat. It adds weight to the rear of the boat changing the center of gravity (CG), which can help raise the bow and allow the motor to run in cleaner water. too far back, you may need to trim under for maximum speed and the boat might hook easier due to the steering leverage being moved further back from the boat's designed turning point. “Air Entrapment” in outboard boating provides a boat with more lift and reduces hydrodynamic friction from the water. Since water is about 800 times denser than air, drag forces are greater, slowing the boat as it moves through the water. Air entrapment can be improved with the right propeller for different outboard applications. These propellers can improve performance on air-entrapment tunnel hulls, multistep, monohull, and V-bottom designs. Yet, too much air entrapment can also cause split-second blow-outs or worse a blowover. “Number of Blades” on a boat propeller can affect its speed, efficiency, and grip. 3-blade propellers are generally more efficient and have better top speed. However, 4-blade and 5-blade propellers have more blade area, which can provide better hole shot and handling at speed but the added drag can decrease speeds. However, the additional blades can also provide more lift and water displacement. 4-blade and 5-blade propellers can get you on the plane faster and at a lower RPM. 5-blade propellers require more power to swing and work best on the newer more powerful 4-stroke outboards 300 HP or greater. "Gear Ratio" with a 1.75 the engine driveshaft needs to turn 1.75 times to turn the prop shaft just one complete revolution (e.g. 1.75:1). A 1.62 ratio the engine turns 1.62 times for every revolution of the prop shaft, (e.g. 1.62:1). Drags racers prefer 2:1, which is simply two revolutions of the driveshaft vs one for the prop shaft. A higher ratio = more engine vs. prop shaft rpm's. Top-end racing applications such as Super Speedmaster (SSM) lower units are closer to 1:1. "Throw a Blade" is a term used in boating to describe when a propeller blade breaks off while the propeller is spinning. The blade may fly off at some speed, hence the term "throw". If a blade is thrown, it can feel like you've lost a transmission. The boat will slow down and vibrate pretty badly and will stay that way through your throttle range. You will also lose handling, it may feel like you've blown up your powerhead. Yes, it's dangerous, also check your prop before running for imperfections and tiny cracks that can lead to big breaks. "Can you Swing It?" refers to a propeller with too high a pitch that can cause a boat to have slower acceleration and lower top speeds. A propeller with too high a pitch can also cause the engine to "lug" or not reach the bottom of the recommended WOT RPM range. This can put stress on the engine and gearcase components. A propeller with too high a pitch can also cause lower-horsepower engines to bog down. This can wear down internal engine parts that aren't built to withstand that kind of stress. "Blow Over" is when a tunnel hull, catamaran, or hydroplane race boat suddenly goes airborne and flips. Blowovers are common for hydroplanes because the hull is designed to generate lift to skim over the water. A blowover can occur when something unbalances the forces that keep a boat on the water; such as a sudden gust of wind, a reduction in downforce, propeller angle, and rough water conditions. When this happens, the front end of the boat lifts too far and the control surfaces can't counteract the sudden increase in lift. The boat can quickly fly into the air and backflip. Blowovers are more rare among deep vee-bottom hulls. "Blow Out" occurs when the ratio of air to water around the propeller is so high that the propeller is no longer grabbing water. Instead, the propeller is trying to propel itself through air or a relative vacuum. Blowout can be caused by the prop running too high, vent holes being too large and allowing too much air to the prop, trimming up too far or cornering, or exhaust gases in a low-pressure area at high speeds. Blowout can also be caused by a rapid change in water pressure along the blades of a propeller. This can cause the water to boil, creating thousands of tiny air bubbles, and cavitation, that burst on the surface of a propeller blade and side of the gearcase. "Porpoising" is the repetitive motion that causes a boat's bow to bounce up and down out of the water. It occurs when a boat won't trim properly. The boat bounces, alternating between diving and lifting as it compensates for the trim problem. To stop porpoising, you can try to trim down or speed up. You can also try to add more or shift weight further forward. Another common cure could be to find the correct prop, pitch, and or engine height combined with the right trim settings at speed. "Chine Walking" is a chain reaction that occurs when a boat is running at high speed, usually 65 mph or higher. The boat falls off to one side and then flops back to the other. This is because the boat is trying to run on a very little hull.  Chine walking is caused by a boat's roll balance instability, engine torque, rotation of the prop, and the hull lifting out of the water as speeds increase. Chine walking is more likely to happen with deep-V and "padded" bottom boats and can be exacerbated when trimmed. "Over Trimmed" in boating means that the trim tabs are too low, forcing the bow down. This can cause the boat to veer suddenly, especially at high speeds. "Over-trimmed" in a high-performance outboard boat usually means the motor is kicked out too far, making the boat unstable. The boat may skate around with reduced steering capacity and the bow may lift and drop in a phenomenon known as "porpoising" or even "blowing over", which are terms we cover here as well. Trimming up too much can also make it harder to get on the plane and reduce top-end speed. "On the Pad" is the flat and/or bottom running surface of a V-bottom boat. When a boat is trimmed up, the pad is the part of the boat that is in contact with the water. At high speeds, the boat rides on the pad, with little or no hull in the water. The pad allows for a more efficient planing surface, which increases the boat's top speed when optimal flying "On the Pad! “Prop Walk” is the tendency of a propeller to push a boat's stern sideways. It affects most single-engine vessels. For example, a single right-handed fixed propeller will tend to push the stern of a vessel to starboard when going forward and to port when going in reverse. Prop walk is also known as the paddlewheel effect. "Standing It on Its Tail" in boating can refer to getting water out of a boat. For example, if a boat is full of water and the bilge won't drain, you can try standing it on its tail to get most of the water out. High performance boaters do this while running the boat, or maybe by accident getting the bow way too high in the air. Weed "Wacker" is a two-stroke engine internal combustion engine that completes a power cycle with two piston strokes during one crankshaft revolution. This is different from a four-stroke engine, which requires four piston strokes to complete a power cycle during two crankshaft revolutions. It is possibly intended to be a derogatory comment coming from inboards when referring to outboards but it's taken as natural affection.