How to Troubleshoot a 1987 Big Bear 350

The 1987 Big Bear 350 is the first 4x4 ATV that Yamaha produced. It features a 350-cc, 4-stroke engine with a hi-lo range, 10-speed transmission. This is a powerful machine with numerous components to maintain. Run through a basic troubleshooting checklist and look out for clogged fuel systems, defective spark plugs, corroded batteries and dirty air filters. Check your owner's manual for a more comprehensive troubleshooting and maintenance checklist.

Things You'll Need

  • Spark plug socket wrench
  • Petroleum jelly
  • Wire brush
  • Screwdriver
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Instructions

    • 1

      Verify that there is sufficient fuel in the tank if the ATV will not start. If there is fuel, check for a clogged fuel cock. The fuel cock is near the fuel tank, and controls the gasoline supply. It has three positions: "On," "Off" and "Reserve." Turn the fuel cock to the "Off" position. Remove the fuel pipe. If there is no flow of fuel, clean out the fuel cock. Turn the fuel cock to "Reserve" if the fuel level is low. Restart the engine. Replace the fuel if it has been sitting for longer than 30 days, as this could contaminate it and create difficulty in starting the engine.

    • 2

      Remove the spark plug with a socket wrench and check the electrode if you experience difficulty starting the engine. Wipe the plug with a clean cloth if it is wet. If the plug is dry, attach the plug cap and hold, or ground, the plug to the ATV chassis. Attempt to start the engine with the electric starter. If the spark is strong and blue, it is good. Replace the plug if the spark is weak or yellow in color.

    • 3

      Check the battery cells for adequate fluid if the engine turns over too slowly. Replenish the cells with distilled water if necessary. Inspect the battery connections and terminals for dirt or corrosion. Use a wire brush to clean the terminals until they shine. Use a small dab of petroleum jelly to lightly coat the terminals to prevent further corrosion.

    • 4

      Replace the headlight bulb if it burns out. Unscrew the headlight cover and the headlight unit assembly. Turn the bulb holder counterclockwise to remove the old bulb. Insert the replacement bulb and turn it clockwise. Reinstall the light unit assembly and adjust the headlight beam if necessary. To raise the beam, turn the adjusting screw clockwise. Turn the screw clockwise to lower. The adjusting screw is on the bottom of each headlight unit.

    • 5

      Clean the air filter element if the engine has difficulty starting. Remove the ATV seat and air filter case cover. Remove the air filter element by lifting it out of the guide. Gently wash the element in soap and water. Squeeze the excess out of the filter and allow it to dry. Apply a thin layer of foam air filter oil, or motor oil, to the element. Reinstall the element to the element guide. Replace the air filter cover case and ATV seat.