My 07 Yamaha 450 died on a trail ride. I was able to bump start it, but ran like crap. I changed the fuel, plug and verified the timing was correct. It will intermittent start and run with no consistency. When it runs everything is normal and then it will die and will not start. It has spark, is getting fuel and seems to want to start but will not run. I am thinking it is the carb. Any ideas?