I am hoping that I can get some help or direction here. My son is just starting to get into racing. He is riding a Bomb. DS90 2 stroke. I have done the following performance mods in hopes of getting some more power/speed out of it. I have ditched the stock airbox for a K&N filter, I installed a pipe from Performance Pros, I had D&D shave the head and port the cylinder. After these mods I found that I needed to re-jet. So after much trial and error….I wound up with about a 149 main jet, and I also drilled out the needle seat with a #50 bit to open that up a little. With the back wheels off the ground, it seems to rev to the high heaven. But during the races, it seems like it is bogging down a bit. It seems to hit sort of a "power band" or starts to rev a bit higher, but that seems to come on too late. I want that to hit earlier and stay on longer.
Any ideas?
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Sounds like you need to work on the CVT clutch... Springs and roller weights.

Bryce

 

You didnt mention any clutch work. I agree that you may need some work in that area.
Whats D&D have to say? Do they think it's running the way their motor work should? I mention this cuz it does sound like the motor work may or may not be working properly.

 

If you're running the stock clutch setup, that's definitely where the problem is. The CVT "shift-speed" needs to be readjusted to coincide with the motor's new power peak rpm. Likely, the stock clutch setup is holding the motor at too low an rpm. With the wheels off the ground, the trans quickly shifts into high gear (without load) and seems to rev easily. But with load on the clutch it holds the revs to ~6-7k until the clutches run out of adjustment, and then the revs briefly sweep through the motor's new sweetspot on the way to redline. You should probably notice that the revs hold and the quad seems pretty sluggish while initially accelerating, then finally really "gets it" at the top end.

Check this article out- clutch tuning