There is no doubt that the 125cc water-cooled Rotax Max TAG (Touch and Go – electric start) categories has the most popular classes in the UK from the more traditional 100cc air-cooled two-stroke that is Formula TKM but they are now challenged by the newer X30 classes. Drivers can start racing in Rotax MiniMax or MiniX from the year of 12th birthday or Junior TKM at age 11, then move into the more powerful Junior Max or Junior X30 at age 13 (or year of 13th with prior experience). Being a TAG class, the Rotax and X30 have an electric press button start whereas the TKM can be either lifted and pushed, or use an optional plug in portable electric start box or use the TAG electric start option which is becoming very popular. Rotax and X30 are more expensive initially but the engine runs longer between rebuilds, so the running costs can be less. The TKM’s are at the economy end for initial purchase with strict price controls. Top speeds in the junior classes vary from 55mph to 75mph. The best advice here, as in all classes, is to visit your local circuit to see what is popular in your area. Drivers in the 11 year old junior classes must weigh a minimum of 38kg with suit, helmet and boots. At 13 it is usually 40kg for the more powerful classes but check class regulations in the MSA Kart Race Yearbook.
MiniMax (Year of 12th birthday-15 yrs) is the lowest powered class of the Rotax family, and uses a very restricted 125cc 2-stroke TAG engine. All Rotax engines are sealed and have a log-book showing the service history. There is an ABkC National Championship in the Super One Series.
By taking the restrictor out of a MiniMax it is converted to a Junior Max (age 13-16 yrs). It is one of the most powerful junior classes, with top speed about 70 mph. There is a ABkC National Championship in the Super One Series.
Junior TKM (11-16 yrs) is a popular traditional kart class using a BT-82 piston-port engine to a strict non-tuning regime. The junior engines have a choice of restrictors between the carburettor and the engine to limit the power, the choice depends on the driver weight. There is an ABKC MSA National Championship in the Super One Series.
Junior TKM 4-Stroke
Tal-Ko, who make the TKM engines, also make a 200cc long-life 4-stroke. Not raced at most clubs currently. For 11- 16 yrs with a senior equivalent.
MiniX (Year of 12th birthday-15 yrs) is the lowest powered class of the X30 family, and uses a very restricted 125cc 2-stroke TAG engine. By changing the carburettor and some components it can be converted to a Junior X30.
A new class from 2014, using a TAG unsealed engine and offering similar performance to Junior Max. There is a national championship in the Super One Series
The premier British championship class for 12-16 yrs (or younger for experienced drivers racing in the CIK events). Also raced at European level not a class for theinexperienced. This is raced in the UK as the MSA Junior British Kart Championship in the Super One. The karts do not have electric starts but are easily push started with a de-compressor valve assistance.
Junior 4-stroke classes
There are other 4-stroke classes for Junior and Seniors which run at certain clubs only e.g. Honda classes and World Formula (senior only). More information on https://www.msauk.org/Resource-Centre/Technical-Kart