Sorry, I didn't mean to mess you guys up!!

In hindsight, the thread pertains to what can be done to improve the performance of the Zongshen NC250 engine.

I'll reitterate my original thought- buy the bike for what it is.

At $330 the big bore kit might be an interesting upgrade down the road for those who are interested.

I've messed with mine about as much as is available.

I whacked off the muffler (and cat) and put on a free flow unit. I feel it helped somewhat on the torque.
Then I put on an Uni, then a K&N air filter. Zero noticeable difference on the butt dyno so I went back to stock.
I think these things are pretty limited by the lack of mapping options. I can't help but think that more gains can be had with the carbureted units that are out of country.

My experience with bore kits all else left alone is not a whole lot more horsepower, but a wider powerband and peaks at lower rpm. I expect the difference to compare to that between Honda's 100 and 125 cc singles from the early '70s. Only 0.5hp gain claimed, but the 125 was much gentler to keep in the powerband, more competent with loads and increasing grade. Same way with the TW200 and TW225 Yamahas.

Lots of complaints about the RX3's cammy nature, this might be a cure. I expect the big bore will complement the EFI. My experience with street EFIs is most are versatile enough to adjust themselves to a few more CCs. CSC has already provided us a decent curve, I don't expect the bore will screw it up. I can think of several dozen other more desirable upgrades that would cost the same or less than new programming.

Lots of complaints about the RX3's tall final drive, with limited options of sprockets not prone to more rapid wear, powerband wider and at lower rpm might contribute to a cure, especially making a couple teeth on the wheel sprocket ideal with the stock 14 countershaft for those of us who do long miles. I expect hard core offroad to still be a lot better with a 13, but I don't do that type riding with my RX3.

Thinking about it, I'd like to have a bit more performance on the highway, but I really don't want the extra weight of the RX4. I expect this bore kit, perhaps with a little port polishing to retain top end, but no porting that would kill the lower powerband, will be the compromise that moves the RX3's position in my garage up a notch or two.