Thank you very much for the conversation and advice. I am being told locally by a mechanic that a "typical" sprocket modification is a "one down (f) two up (r)". I thought that would leave the resultant number at 13/47 which I was told would not be quite "stunt" dramatic, but would pull much more low-end torque for quick, local riding. I have not discussed the front sprocket change causing a chain guide rub with him yet.
About the air, get a drop-in high flow filter (keep the air box), full exhaust, and jet kit the carb? Is that right?
Yes the "typical" sprocket mod to get the bike to exhibit more torque is to go down 1 tooth on the front and up 2-3 on the rear sprocket. Also the "typical" bike this is done on already has a ton of HP and torque to begin with and comes stock with either a 15 or 16 tooth front sprocket.
The Ninja 250 is not the typical bike as it neither has very much HP, torque or a stock 15 tooth front sprocket. That is why during your research you probably did not find too much about a 13 tooth front sprocket, but a lot about a 15 tooth. If you really think about it, the Ninja 250 is already geared too low (under geared). It actually (wastes) does not utilize the HP it has to it's full potential. Gearing down any further, not only will you lose top end speed but some in between. What you will get is an engine that's revving crazy high, with a slight bit of pull in 1st gear that's going nowhere. Use Gearing Commander
to help you figure out your gearing.
With a good drop in filter
like the Pipercross or Hurricane, a full exhaust and jet kit, you'll get a slight increase in HP and torque on the low end. For that fact even shimming the needles will help with a better throttle response.
The key is finding out were your power comes on. 1/4 throttle (3k rpm) is where you really start to see more fuel added to the mix. This is also a good launch speed. The Ninja 250 is never going to be a bike that has any significant amount of low end torque.