How to Re-Jet a Yamaha Blaster

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Your Yamaha Blaster's carburetor uses a series of small nozzles, called jets, to meter fuel and air to the motor at any given speed. As it comes from the factory, the carburetor's jet configuration is suitable for most riding situations. The addition of a high-performance exhaust and intake system, or riding at an elevation higher than 5000 feet above sea level, requires a change from the original jetting. To make these changes, you will need to remove and partially disassemble the carburetor. While re-jetting isn't too difficult, it may take several attempts before you find the correct jet configuration.

Things You'll Need

  • #210 or 230 Main jets
  • Gas can
  • Flat and Phillips screwdriver
  • 8 mm socket
  • Socket wrench
  • Pliers
  • Determine what changes need to be made to the carburetor's main jet. The stock configuration uses a #220 main jet, which is ideal for an unmodified Blaster ATV. Obtain a #230 main jet (one size larger than stock) to add more fuel to compensate for increased air flow generated by a performance exhaust and intake system. Alternatively, obtain a #210 main jet for reduced fuel flow to compensate for air pressure differences found in higher elevations.

  • Determine what changes need to be made to the jet needle's position, if any. The jet needle is on the bottom of the carburetor's throttle valve and controls fuel flow from a quarter to three-quarters throttle. The needle has a tapered profile that narrows at its tip, increasing the amount of fuel metered into the carburetor as the needle is lifted by the throttle valve. A small e-clip, placed in a series of grooves cut into the top of the jet needle, raises or lowers the needle to alter fuel flow. In its stock configuration, the clip is positioned on the second groove from the top. Raising the clip lowers the needle to reduce fuel flow. Likewise, lowering the clip will raise the needle and increase fuel flow. In most cases, the jet needle will only be repositioned to fine-tune the ATV's performance.

  • Turn the fuel valve on the left side of the ATV's gas tank to the Off position. Follow the fuel line on the back of the valve to the left side of the carburetor. Pull the line off the carburetor and drain any remaining fuel into a gas can. Pull the oil hose off the rear of the carburetor. Unplug the electrical connector from the front of the carburetor.

  • Loosen the clamps securing the carburetor to the air box and the motor, using a Phillips screwdriver. Pull the carburetor away from the motor. Unscrew the drain screw from the left side of the float bowl on the bottom of the carburetor with a flat screwdriver. Drain any remaining fuel into your gas can. Twist the carburetor's top cap-and-throttle-cable counterclockwise by hand, you can pull it away from the carburetor. Grasp the throttle cable and then pull it away from the carburetor to remove the throttle valve and its spring.

  • Flip the carburetor over, bottom facing up. Remove the screws from the float bowl on the bottom of the carburetor with a Phillips screwdriver. Lift the float bowl off the carburetor to reveal the main jet, in the center of the carburetor's float chamber. Unscrew the main jet from the carburetor with an 8-mm socket and a socket wrench.

  • Screw the new main jet into the carburetor with an 8-mm socket. Re-install the float bowl, using a Philips screwdriver to tighten the float bowl screws.

  • Pull the throttle cable, the valve spring and the jet needle out from the top of the throttle valve. Pull the clip off the jet needle's grooves with a pair of pliers. Reposition the clip to a higher groove on the jet needle to decrease fuel flow, or to a lower groove to increase fuel flow. Re-insert the jet needle into the throttle valve, followed by the throttle cable and the valve's spring. Slide the throttle valve into the top of the carburetor. Slide the top cap down the throttle cable until it rests against the top of the carburetor. Screw the cap onto the carburetor by hand. Skip this step if you will not be changing the jet needle's position.

  • Press the carburetor into the motor's intake boot and tighten the boot's clamp with a Phillips screwdriver. Push the air box's boot over the opposite end of the carburetor. Tighten the air box's clamp with a Phillips screwdriver. Push the fuel and oil lines onto the nipples on the left side and rear of the carburetor, respectively. Plug the electrical connector into the front of the carburetor, near the air box's boot.

  • Start the ATV and allow it to warm up completely, then take it for a test ride. Take note of any flat spots -- a sudden hesitation or decrease in power, often caused by too much fuel -- in the ATV's performance. If flat spots occur, lower the jet needle's position by one notch to decrease fuel flow, and then test ride the ATV again.

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References

  • "The Professional Motorcycle Repair Program"; Professional Career Development Institute; 1995
  • "Yamaha YPS200 Service Manual"; Yamaha Motor Corp.; 1987
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