Shifter Go Karts are a type of kart that come with 125cc engines from bikes and usually have a sequential transmission going up to 6 speed. A driver of this go kart can get up to 60mph in under four seconds which even a lot of actual cars cannot manage. Their top speeds are around 125 mph on a long straight section of road or track. They are best on flat tracks though as they do not come with any suspension.
At the front of a Shifter kart are disc brakes and at the back is a single disc which allows for excellent braking and the ability to take corners very well. A driver taking a corner can reach lateral forces of up to 2.5gs. While they are particularly popular in the US, in Europe, including the UK, the preferred type is more the 125 cc or 100 cc engine types. You can find 125 to 250 cc Shifter go karts though in certain categories of racing.
If you are used to driving automatics or something without gears, you will need to learn how to change gear, and when it needs doing. It is not easy so when you first start driving one but do not give up, just keep practicing. Once you have learned how and picked up the signs of when to change you will even wonder why you ever struggled! If you are having a manual transmission on a go-kart use something lighter and smaller.
If you are going for an automatic go kart transmission like a CVT this would be for a kart of a max of 200 ccs. CVT stands for Continuously Variable Transmission and is also called a shiftless transmission. There are some disadvantages to this option though, comparing the belt drive and the gear drive, the former is less efficient and in general, you want the opposite to be true in go-karts. CVT can be a bit heavy in some cases and is not always cheap. It also needs tuning and to do that a person needs to know what they are doing.
There is also a more powerful DSG or Direkt Schalt Getriebe (German) which is a dual clutch and multiple shaft gearbox allowing automatic or semi-manual selection of gears. This, in general, is not as feasible as a CVT though because most karts are not that powerful.
It is important to get the shifter go kart transmission right as it has an essential role in maintaining top rpm while ensuring the engine does not overheat (which could lead to an explosion). Alternatively, you could use a centrifugal clutch with sprocket making sure you first work out the proper gear ratio needed for the best acceleration and reaching top speeds. Find out how does a go kart clutch work. It is lighter than the CVT and could save you money.