Anecdotal sources suggest that you can adjust your 99 Arctic cat 300 4x4 valve to .004 (intake) and .006 (exhaust). It will allow the bike to start easily.
But please note to check with an authorized Arctic Cat dealer to be sure the same info applies to your model. As there are some that run .003 on the intake and .005 on the exhaust.
Proper valve lash is key in helping the quad not only start, but run properly. If the valves are too tight, the valves will not close fully and you'll lose compression. If they are loose, they won't open properly.
With proper care and maintenance, an ATV can last forever. Check out these 10 tips to extend the life of your ATV shared by Gameandfishmag.com.