I had the same problem about 12 years and definitely it was the CDI at a cost (parts only) more than $300. I reluctantly ordered the CDI since my machine was virtually new with very little usage however, that corrected the problem and it ran good for maybe 25 hours over the next year then failed again. The ATV has been sitting behind the shed ever since. I was told at the Yamaha service shop that this is typical for the machine. I could not further justify investing $$ for such short life expectancy. The part sales now closer to $500.