Tusk Fuel Mixture Screw Installation & Tuning Video

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Tusk Fuel Mixture Screw Installation & Tuning


This video covers the installation and tuning for the Tusk Fuel Mixture Screw.

The Tusk Fuel Mixture Screw replaces the stock fuel screw found on Keihin FCR carburetors. The purpose of the fuel screw is to effectively adjust the fuel/air mixture at lower RPMs, which would be ¼-throttle or less. The stock fuel mixture screw is difficult to get to and adjust, but the Tusk Fuel Mixture Screw makes this an easy task.

The screw requires no tools to adjust since it extends from the carburetor, and features an easy-access knob. The screw comes complete with the sealing O-ring, tension spring, and washers. It's made of precision machined 6061 T- 6 aluminum, and has laser-etched numerals on the knob that aren't going to rub off. These laser-etched numbers allow for accurate adjustment, to keep the throttle response crisp and clean. The center O-ring keeps dirt out and reduces vibration for accurate performance.

To install the Tusk Fuel Screw, it's simple: You just remove your stock screw and replace it with the Tusk Fuel Mixture Screw. One note when removing your stock screw, make sure the stock spring, washer, and O-ring come out with it. Please note that it also may be necessary to loosen the clamps on your carburetor and rotate it so you can gain access to the stock fuel mixture screw. It's a good idea to refer to your service manual for stock settings and adjustment information. Most stock settings are around 1½ to 3 turns out. Small adjustments in or out can improve throttle response off idle. Remember that the further the screw is turned out, the richer the fuel mixture will be.

Once we've got the stock fuel screw out of the way, we can just thread the Tusk Fuel Mixture Screw up into place. You'll feel the O-ring seat; you don't want to go any farther past that, that's where you want to stop. Once you get to that point, we're going to start threading it back out, and set it back to stock settings. On this bike it happens to be 2 turns out.

We've got the Fuel Mixture Screw at stock settings, but we may need to slightly adjust its position to get the desired setting. To do that, we want to have the motor warm and running at a high idle. We're doing to start the bike and adjust it to a high idle. Once the bike is warm, we can begin making our adjustments. We're going to turn that screw in until the engine stumbles and almost dies. From there, we want to pay close attention to the RPMs of the motor. While counting turns, backs the screw out until the RPMs of the motor peak. Once we've found that sweet spot, we want to record that for future reference. If you go too far out, the engine won't sound as smooth. Then we're going to set the idle back down to normal. Then we're ready to go ride.

Remember, temperature, elevation, and other factors will adjust this setting, but adjustment is made simple with the Tusk Fuel Mixture Screw. Whether you're running a spark arrestor up in the mountains or running it wide open out on the track, making this adjustment will be simple.

The Tusk Fuel Mixture Screw is a great upgrade for any Keihin FCR carbureted 4-stroke. Get yours today at RockyMountainATV.com.