I've used one of these and was able to turn upwards to 10,000 rpms. Most likely your experiencing valve float . It's typical of the small valve stock heads. Depending on the manufacturer and the age of the head ( springs get weak), you might not be able to see much over 8500,
Many years ago there was this electronic geek over at BN who attempted to discover (at the time it was a rumor that rev limits even existed) which cdi's did indeed contained a limit. There wasn't all these aftermarket" high performance" offered back then. Fellow members sent him cdi's from various models to test. If I remember correctly, or not, he found two out of about 6 that did contain a actual limiter. Don't quote me on this, it was almost ten years ago and my memory sucks. There may still be the thread in the archives over at BN. I do remember that a limiter was discovered and we were surprised at the low percentage of the test batch that actually contained a limit.
my point is.. don't dismiss that cdi yet, take a look at up grading the valve train.
Also consider these motors use a huge amount of fuel to run at high rpms. you may be jetted fine for low to mid range or normal riding but your running out of gas when it really turns up.
Kind of a tough call to make as all three, cdi, valve train, and fuel all give similar symptoms, the motor reaches a certain point then runs flat.
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