By: George Robinson
The Rotax MAX was introduced in 1997. Direct drive karting was predominately 100cc in three basic types, reed, rotary and piston port induction. These classic engines formed the backbone of club, national and international racing. Leisure karting grew up around the 4-stroke Honda GX used almost exclusively in indoor karting. In the quest for more speed these leisure karts soon had twin engines and tuning aids forming the next step up from the arrive and drive corporate entertainment market.
This potentially huge sector of the new karting public were not the same as the professional and enthusiastic amateur drivers who raced 100cc. Either by very clever market research or partly by mistake Rotax hit on the product to unite these diverse karters. The reason the MAX has been so successful is due to its user friendliness and aggressive pricing. In simple terms, an engine that is delivered complete with all accessories, a clutch and self-starter for about the same price as a contemporary 100cc unit has to be a winner. I believe that even without the arrival of the MAX, 100cc karting was in trouble anyway and badly needed a new image. There is no doubt that a good 100cc kart is still a very fine driving experience, described by Ayrton Senna as the purest form of motorsport after he had won the Formula 1 World Championship. This is something the MAX will never be.
The MAX was not designed as a competitor for 100cc engines, in fact Rotax continued to manufacture 100s for some time after the introduction of the MAX. In many countries the MAX was not affiliated into their national classes and remained in the leisure categories. However market force is the strongest element to make something happen even when the governing body may be at odds with the particular line of evolution. I remember a powerful mover and shaker in the 100cc classes saying that the MAX might become popular but that it would never run in Super 1. This year the MAX classes have easily the highest number of entries at Super 1. The Rotax MAX has evolved over the past seven years from a slow start to such excessive demand that supply just could not keep up. The engine unit has been improved in terms of production quality and consistency but a well maintained early
engine will still perform well enough to win at club level today.
There can never be a win/win situation forever and without doubt there will eventually be something that takes over from the MAX. It may be another Rotax product, if so it will almost certainly be a 4-stroke. However, for the time being the Minimax, Junior and Senior formats are very much here to stay and will be so for many years to come. The long term future may well be 4-stroke but this is a fundamental change for karting and one that will not be an easy transition in my opinion. A high performance 250cc single cylinder engine sounds to me very much like one cylinder of a Formula 1 engine. To be efficient and produce low emissions it must have electronic engine management and fuel injection with the potential to drive costs through the roof.
Design and production of a racing 4-stroke has to be of a far higher standard than a 2-stroke of similar performance, the maintenance costs are also bound to be greater, there are a lot more moving parts. A performance 4-stroke has a high maintenance valve train and there is no escaping that. I do believe it will happen to karting and probably within the next ten years but there will be space for 2-strokes for a long time to come. There are so many people involved in karting today who would never have known about it years ago, simply because public awareness has increased dramatically. I remember a survey during the 1990s. The statistic I will never forget was that 1.25m people a year drive karts in Britain but that only 3% are MSA licence holders, oh dear! Again the MAX scores. So many are used by hobby drivers who have a great time, charging round at weekends racing their mates, but who never aspire to racing officially.
These participants are clearly valuable to the industry. They do not account for 97% of the business since their karts are often maintained to a very basic level, but their contribution is nevertheless significant. I’m sure the majority of this magazine’s readership is the MSA racing minority, the rest are the people supporting the racing fraternity indirectly by providing homes for last year’s racing equipment. This section of the karting public is often overlooked and need to be encouraged to stay in the sport and aspire to participating at MSA level. On the technical front this month, I want to revisit the old chestnut of carburettor jetting.
Those of you who know it all or cannot believe I am about to say the same things again, please feel free to turn to another page. As a result of writing this column I receive a number of telephone enquiries from people in trouble of some sort with their MAX engines. Carburation is by far the most popular subject. Regardless of class the same Dell’Orto 34VHSB carburettor is used but the three MAX class engines all demand a different carburettor set-up. The Senior engine needs to rev up to 14,000rpm, the
First in the World for 44 years
Junior up to 12,500 and the Minimax up to 11,750. These are broad figures and I know plenty of people claim much higher rev values. These are generally accurate figures that don’t allow for revs increasing when leaving the ground or when there’s a following wind on the fastest straight. As a guide you need to see rpm readings within 1000 of the above figures to be competitive. High revs are found by near ideal jet settings. If the jet is too big, the engine will not run clean at higher revs, however if the jet is too small the Junior and Senior engines will pop back through the exhaust and may lack mid range power.
There is usually a reasonable band of jet sizes within which the engine will run satisfactorily, it is also true to say that there are carburettors that react more to small changes than others. The Minimax with its 2004 restrictor in the exhaust only, certainly needs a much smaller jet. For example, an average jet size for a Senior might be a 162, on the same day with the same conditions and a similar carburettor a Junior might run a size or two bigger at 165 or 168, a 2004 Minimax on the other hand would require something between 145 and 150. It is worth reminding everyone that for MSA racing the carburettor must now be completely standard. People are still being caught using non-standard slow jets and needles. Unfortunately rules are rules and they are there to make the playing field as level as possible for everyone, there can be no excuse for running illegal components.
The only part that may be changed is the main jet, the needle may also be adjusted for height. Both the 8.5 and 12.5 venturi models are eligible but others stamped 9, 11, 13 or anything else for that matter are not original equipment and cannot be used. The exhaust must not be ignored, the life expectancy of the baffle tube and wadding is 10 hours, this is easily overlooked and can lead to unexplained loss of power as the inner end of the perforated tube starts to decompose allowing the wadding to implode, partly blocking the exhaust outlet. When fitting the new baffle and wadding I prefer M4 button head bolts with nylock nuts to rivets. It is worth checking the whole exhaust for cracks and damage. It is now acceptable to repair by welding the exhaust providing this does not change the original specification of the system in any way.
The new season of racing is well under way with club and championship meetings into their second and third rounds. The usual cries of ‘cheat’ and ‘foul’ are heard rumbling around the pits, the majority being unfounded but rest assured that JAG do take these reports seriously and expend a lot of time and money ensuring the classes remain as fair as possible. Next month I hope to bring you details of impending Rotax RM 1 test days. Also a look inside a MAX engine after years of trouble free running.