How to Adjust Idle Speed on Mercury V6 2-Stroke Outboards (1976–2005) Adjusting the idle on a Mercury Marine or Mercury Racing V6 2-stroke outboard —including popular 2.0L, 2.4L, and 2.5L  models ranging from 150hp to 300hp —is essential for smooth performance, better fuel economy, and consistent gear engagement. Whether you’re working on a classic 150hp XR2 , 175 Black Max , 200hp carb model , or a high-performance 2.5 EFI 260hp , proper idle speed keeps the engine running cleanly at low RPM and prevents stalling during shifts. Idle speed varies based on the testing environment. When the outboard is on the hose  (out of water) and in neutral , expect the engine to idle roughly 100–200 RPM higher  than it will in real-world conditions. That’s because the lower unit isn’t submerged, and there’s no exhaust backpressure , which lets the engine breathe easier. While this setup is fine for warm-up, it’s not accurate for idle tuning. When the engine is in the water and in neutral , the exhaust exits through the submerged hub, creating more backpressure and causing the idle to drop slightly. For precise tuning, you need to adjust the idle in gear , with the propeller and lower unit fully submerged . This is when the engine is under load and replicates how it will behave during actual operation. Shift into forward gear and use a reliable tachometer  to check idle RPM. Most Mercury V6 2-strokes—including the 200hp Offshore , 225 Promax , and 2.5L 280hp —should idle between 650 and 750 RPM in gear , depending on the application. High-performance models like the 2.5L 300 Drag  or 245 Carb  tend to idle on the higher end to stay crisp off the line. How to Adjust Idle – Refer to Diagram Refer to the labeled diagram above. The key adjustment point is screw “c” , which is the idle pickup timing screw . This screw controls the throttle plate position at idle and effectively sets your base idle RPM. To adjust: Loosen the jam nut (b)  that locks the screw in place. Turn screw “c”  clockwise to raise idle RPM or counterclockwise to lower it. Once the desired RPM is reached, retighten the jam nut to secure the setting. Note: Many mistake screw “a”  (idle stop screw) as the primary adjustment, but in these V6 2-stroke setups, especially on high-performance or carbureted models, screw “c” is the correct one  to set idle speed. Screw “a” is more commonly associated with neutral stop settings. If RPM still fluctuates or idle isn’t stable, check for vacuum leaks, fouled plugs, or dirty carburetors. Many Mercury models like the XR6 150 , 200hp Bridgeport , and 225 EFI  perform best when carbs are synchronized and fuel delivery is clean. Environment-Based Idle Behavior: Out of Water, Neutral (on hose):  It should idle 150–200 RPM too high In Water, in Neutral:  The RPMs will drop slightly due to backpressure In Water, In Gear:  This is the most accurate to ensure it runs under load Proper idle adjustment improves throttle response, minimizes plug fouling, and ensures smooth shifting and acceleration. Whether you're running a vintage Black Max 200 , a 245HP Carb , or a modern Mercury Racing 280 ROS , taking the time to dial in idle speed pays off in performance and reliability. Always reference your specific service manual for exact idle RPM targets and safe adjustment procedures.

different size wrist pin washers and needle bearings are used for top vs bottom guided connecting rods In two-stroke engines, “top-guided” and “bottom-guided” refer to how the lateral movement of the connecting rod is controlled. In a top-guided connecting rod, the small end is tightly confined at the piston pin (wrist pin) area. The rod fits snugly between the piston bosses, often with thick steel washers or spacer shims on the wrist pin, which nearly eliminate side-to-side movement. This setup allows the rod's big end to have extra side clearance on the crank journal, meaning it can float freely without rubbing against the crank cheeks. As the name implies, alignment is maintained at the top. By contrast, a bottom-guided rod  design leaves more space at the piston pin area, allowing the small end of the rod some lateral play. Instead, the big end of the rod is centered by the crankshaft itself, with minimal clearance between the rod and crank cheeks. In some cases, a wider bottom on the rod restricts the side movement at the crank. This method centers the rod from the bottom end, with the small end moving more freely under the piston. Controlling side clearance is critical because the connecting rod must not be allowed to move excessively side-to-side. Top-guided rods rely on the piston assembly to guide the rod’s movement, while bottom-guided rods depend on the crankshaft to keep things centered. Mercury V6 2-Stroke (1976–1989): Bottom-Guided Rods found in earlier 2.0L and original 2.4L Outboards Mercury’s early two-stroke V6 outboards—specifically the 2.0L and 2.4L models produced from the mid-1970s through the 1980s—used bottom-guided connecting rods . This includes consumer models like the 150HP, 175HP, and 200HP Black Max series, as well as performance variants such as the SST-140, F1, and 2.4L Bridgeport racing engines. These rods are easily identified by their thicker big ends, which fill out the crank journal and have minimal side clearance. The small ends, on the other hand, show noticeable side play under the wrist pin due to the lack of shims or spacers. Notable casting/forging numbers include 8118  for the smaller bottom-guided rods and 5250  for the larger ones. The 5250 rods were sometimes re-machined for top-guided use in racing applications and are known as the “Chatfield” rods, named after the machinist who developed the modification for Mercury Racing. Interestingly, you can still find a few of the Mercury 5250, referred to as the 280 ROS Hi-Perf Big I-Beam Rod in the Mercury Catalog under OEM part number 847522 A9 or 8M0084786 for a whopping MSRP of $710 each! Mercury V6 (1992–Present): Top-Guided Rods found in later 135-200HP and Race 2.5 Liters Outboards With the launch of the 2.5L Mercury V6 two-stroke engines around 1991–1992, Mercury transitioned to a top-guided rod design . This change applied to all 2.5L models from 1992 onward, including both standard production outboards like the 150XR6 and 200HP EFI, and high-performance versions like the 225 ProMax, 260 EFI, 280HP, S3000, and Drag motors. In these engines, the rod’s lateral alignment is controlled at the piston end. You’ll find thick steel spacers or washers on the wrist pin, with the small end of the rod nearly spanning the piston boss gap. This holds the rod tightly in place at the top. Conversely, the rod’s big end floats more freely on the crank journal, with greater side clearance since it’s not constrained by the crank cheeks. Identification is simple: if you see wrist pin spacers and a snug fit at the piston but free play at the crank, it’s a top-guided setup. Mercury’s top-guided rods are typically marked with the forging number 818141 , often shortened to “141” by technicians. Connecting Rod Measurements & Washer Specifications Bottom-Guided Rods  have a big-end width of 0.812 inches (20.59 mm) . These use a stepped washer , with one side stepped down to fit against the connecting rod for proper lateral alignment at the crankshaft. Top-Guided Rods  have a big-end width of 0.712 inches (18.08 mm) . They use flat washers on both sides , allowing the rod to be centered at the piston pin instead of the crank journal. Performance Benefits of Top-Guided Rods Mercury top-guided rods (along with optional 10x stronger ARP Rod Bolts) bring several advantages in modern builds: Improved lubrication : Greater clearance at the big end promotes better oil flow around the crank journal. Reduced friction : With the big end not rubbing against the crank cheeks, there's less drag and lower wear at high RPM. Stronger construction : The newer top-guided rods, like the 818141, are stronger than older smaller "pencil" 8118 bottom-guided rods, making them better suited for higher RPMs, bigger bore pistons, high-performance running and racing applications. While both rod styles are reliable in standard use, top-guided rods offer superior durability, lubrication, and thermal performance —especially important in high-output marine engines like Mercury’s 2.5L V6 two-strokes.

044 Style EFI Pump Flow Estimates at Varying Voltage & Pressures The Buckshot Racing #77 EFI fuel pump, a high-performance Bosch 044-style replacement, is widely trusted for demanding EFI applications in marine and motorsport environments. The spec flow rates for the pump are 79 GPH (300 LPH)  at 43 PSI and 13.5 volts , 67 GPH (255 LPH)  at 43 PSI and 12 volts , and 53 GPH (200 LPH)  at 75 PSI and 12 volts . These values reflect real-world performance across different voltage conditions. Since electrical system voltage varies depending on battery chemistry—lead-acid batteries average 12.4–12.6V, AGM batteries around 12.7V , and lithium iron phosphate (LiFePO4) batteries often sit between 13.0–13.4V —this evaluation assumes a practical baseline of 12.7 volts  to reflect common high performance use. At 12.7V and 43 PSI, the 044-style pump is estimated to flow approximately 71 GPH (270 LPH) . Like all electric fuel pumps, its flow rate decreases as pressure increases, typically by 10–15% per 10 PSI . Understanding this pressure-flow relationship is essential for designing fuel systems for Mercury 2.5L EFI engines, which vary in both fuel pressure and volume depending on model and modification level. Below are a few examples. The Mercury Marine Laser or XRi  type front injected motor requires approximately ~ 26 GPH (98 LPH)  at 33 PSI  at wide-open throttle (WOT). At this relatively low pressure, the Buckshot #77 pump outputs over 74 GPH (280+ LPH) , offering nearly 3× the required flow , ensuring excellent injector supply and pressure stability under load. The Mercury Racing 260 EFI  demands slightly more fuel at WOT, requiring ~ 28 GPH (106 LPH)  at 39 PSI . At this pressure, the pump continues to deliver around 70–71 GPH (265–270 LPH)  at 12.7V, again offering a safe 2.5× flow margin , suitable for high-performance recreational and competition use. The Mercury Race 280 ROS, 300 Drag, and S3000  versions require a higher flow of ~ 30 GPH (114 LPH)  at 56 PSI , pushing the system closer to the high-pressure limit of the pump. At this pressure, flow output is estimated at 58–61 GPH (220–230 LPH) . The pump provides roughly 2× the required fuel volume , ensuring consistent WOT operation with solid headroom. For heavily modified Mercury 2.5L engines  producing 350+ horsepower , estimated fuel demand rises to ~ 35 GPH (132 LPH)  at approximately 56 PSI , depending on porting, RPM range, and final tune. In this case, the 044-style pump, delivering ~ 60 GPH (220–230 LPH) , offers around 70–75% flow overhead , which is generally acceptable for high-output naturally aspirated builds. For ultra-high-performance, a ~110 GPH (400LPH+) pump setup may be more suitable to maintain safe injector pressure and flow margin. In conclusion, the Buckshot Racing #77 EFI pump provides robust flow performance across a wide range of pressure and voltage conditions. With a real-world baseline output of 71 GPH (270 LPH)  at 12.7V and 43 PSI, it is fully capable of supporting all Mercury 2.5L EFI variants—whether it's a stock Laser XRi, a tuned 260 ROS, a high-pressure 300 Drag, and would support fully built 350+ HP motor with the 1/2" input, no bends and no 90 degree fittings are recommended. We would soft bends on your fuel hose to reduce flow distribution including airation in the lines that can be caused by hard bends. With proper voltage management, high flow filtrs, and return-style fuel regulation, this pump delivers consistent performance and headroom even under wide-open throttle and race conditions.