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- - The Kart - - Setup Info - - Starting Karting - - Race Reports - -


The Rotax Max class is one of the UK's non gearbox karting classes. It uses a 2 stroke 125cc Rotax SR125 engine, which is a single cylinder, liquid cooled reed valved engine. This engine has a pneumatically adjusted exhaust valve, centrifugal clutch and an integrated electronic starter for ease of use. Below is a video of a couple of laps of the track at Wombwell, home to South Yorkshire Kart Club.

The engine is used in various states of ‘tune’ in the Minimax, Junior Max and Senior Max classes, the latter being the class that MacG Racing Participates in. Specifications are shown below:



Description of the Kart and technical specifications.

Mini MAX

Junior MAX



54,0 mm


54,5 mm


124,8 cm3


10 kW

15 kW

21 kW


8500 rpm

8500 rpm

11500 rpm


12 Nm

17 Nm

21 Nm

Fuel tank

7500 rpm

8500 rpm

8750 rpm


Dry centrifugal clutch

Intake silencer

Intake silencer with integrated air cleaner


Oil in fuel, high quality 2-stroke oil, mixing ratio 50:1

Intake restrictor



Pneumatic exhaust valve



Weight of engine

Approx. 12 kg (without accessories)

Accessory kit with

Intake silencer, carburetor, fuel pump, exhaust system, radiator, battery, complete cable harness, battery support and battery charger

Optional extras

Rev. counter and temperature sensor


As you can see the Minimax class uses an intake restrictor to keep power down, whilst the Junior Max class leaves the engine with no additions, the Senior Max class has the pneumatic exhaust valve included on the engine to give extra power higher up in the rev range.

Picture of the Rotax Max 125cc Engine

The carburetion is via a Del Orto VHSB 34 QD carburettor, which works in conjunction with a fuel pump. The carburettor is of the fixed jet variety, meaning that changes in mixture can only be achieved by physically changing the jet that is inserted into the carb itself. This can be a black art, however with an accurate weather station, changes in atmospheric pressure and air temperature can be monitored and adjustments to the mixture can be made accordingly.

Chassis are available from a large number of manufacturers. Although the chassis are all manufactured in accordance with strict rules set out by the sports governing body, some chassis do appear to suit some drivers better than others, and some have more adjustability, nicer features etc. You often hear many comments about different chassis’ being suited to different circuits/conditions better than others; the truth is, they may be right! The best way to find out is to test a variety of different chassis and choose the one which gives you the quickest times. Remember that a chassis that feels good may not be the fastest! Macg Racing currently use a Gillard chassis. This choice was made partly due to availability and partly due to the companies many successes at various levels of karting around the world at the time of purchase.

Just Doors UK sponsoring MacG Racing
Millers Oils Motorsport Nanodrive from MacG Racing
CSF Radiators from MacG Racing
Braid Wheels
Wavetrac Differentials from MacG Racing
Quantum Racing Suspension sponsors MacG Racing
Albins Performance Transmissions sponsors MacG Racing
Drenth Motorsport Gearboxes from MacG Racing

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