2008 Yamaha Motorsports Big Bear 400 4x4 IRS Owners Manual - Page 102
2008 Yamaha Motorsports Big Bear 400 4x4 IRS Manual
Page 102 highlights
Specified spark plug: NGK/DR8EA To install the spark plug 1. Measure the spark plug gap with a wire thickness gauge and, if necessary, adjust the gap to specification. Spark plug gap: 0.6-0.7 mm (0.024-0.028 in) 1. Spark plug wrench 8 To check the spark plug 1. Check that the porcelain insulator around the center electrode of the spark plug is a medium-to-light tan (the ideal color when the ATV is ridden normally). NOTE: If the spark plug shows a distinctly different color, the engine could be operating improperly. Do not attempt to diagnose such problems yourself. Instead, have a Yamaha dealer check the ATV. 2. Check the spark plug for electrode erosion and excessive carbon or other deposits, and replace it if necessary. 8-10 1. Spark plug gap 2. Clean the surface of the spark plug gasket and its mating surface, and then wipe off any grime from the spark plug threads.