Re: Straight Issues '95 CBR900rr
1. Do you have new gas in the tank? Drain the old gas out and put it in your car or truck (there is almost definitely a bit of water and a bit of varnish in there, now, and the octane level is down). Put fresh high-octane in the tank.
2. Drain the float bowls - they are often full of crud. Turn the petcock back on and give the float bowls a couple of minutes to re-fill before trying to start again.
3. Pull a spark plug. Does is smell like gas? (It should smell like gas.) Is it fouled with oil? Check for spark (plug it back into the spark plug boot, ground the plug on the engine, turn it over). If it has fuel and spark, it HAS to start (unless it isn't getting air or the timing is out).
4. Check for mouse nests in the airbox and exhaust (I've seen it, more than once).
5. Move the kill switch back and forth a few times, to be sure it has a good contact. Place it in the 'run' position (stupid, but I've seen good mechanics kill a battery trying to start a bike with kill switch off / no gas / spark plug sitting on ground / etc. Happens to the best of them occasionally, and happens to me a lot.)
That takes care of fuel, air, and spark - the timing almost never goes on a modern bike, so it should run now. If you have done everything correctly and it still won't start, just stand and swear at the bike for a few minutes, then go have a drink.