Mikuni TM40 Carb Rebuild Question

Mikuni flat slide rack carbs?

They are very common and a very good carb. Alls u really need to do is pop the bowl off. Make sure u use a good correct size Phillips head on the lone screw, and spin the drain plug off. Take the main, pilot (careful of springs and washers) and starter jet off. Choke plunger out, fuel screw and crab cleaner through everything.

The bowl gasket is o-ring like and easily re-usable. The plastic float assembly isn’t really adjustable, just make sure needle holds pressure.

That’s it. Shouldn't need to go further

Yeah, unfortunately, they don't have a carb kit like you'd find with a common automotive carb. Not sure why since it'd be nice to be able to refresh all the rubber pieces. You can get the pieces through Polaris, but they're expensive.

The TM40 was fairly common on snowmobiles, Polaris used them on the 700s and 800s, several other makes used them too. It's hit or miss whether they need new pieces or not; given the prices, I'd say the best approach is the tear the carb down and see what things look like. If the rubber pieces are intact and not completely hardened up, you should be good to reuse them. A regular cleaning should be all that's necessary (especially if you avoid ethanol) until the pieces start showing signs of distress.

There aren't any upgrades, practically speaking; changing carbs around on 2-strokes, while possible, isn't as straightforward as an old small block.