If you want to ride....and not spend a lot of time adapting, jetting and sorting out a new carb - then the kit from Lancer bolts on and is jetted in the ball park and will start and run right out of the box. I ended up changing the pilot and main jets just a bit to get it perfect.

If you like to experiment and build your own throttle cables and work out the manifold adapter and connection to an air filter,etc., then you can buy something and spend some time trying to get it to run right.  Don't go too big....the engine doesn't flow a lot of air and really doesn't need anything bigger than 36mm with a stock engine.

I bought the VM36 kit from Lancer, and it runs really well.  It works a bit different than the stock carb, the engine responds a bit faster to the movements of your throttle hand, and the backfires and rumbles when slowing down still occur - however it is easy to control the noise by not letting the throttle close completely when shifting or decelerating.  Even with the stock carb you can cut down on the noise a lot by just holding the throttle open a touch when you roll off the throttle.....don't let the throttle slam all the way closed.