I agree 100% with you that high performance four strokes, suchas the Swissauto, Vampire etc have a lot to offer karting particularly to the driver. Their broad powerbands in particular appear to be better suited to the requirements of non-gearbox karting than that of many current two strokes.
However the relatively peaky powerbands and slightly flaccid bottom end response of many two strokes, especially the RPM limited models suchas the Rotax Max are not necessarily a characteristic of all two strokes. A lot of it comes down to the size of the engines used in karting. Rotax kicked off the whole TAG phenomenon by simply taking one of their existing motorcycle engines, the 125cc Aprilia, lopping off the gearbox and sticking it on a kart without many modifications. Obviously from a commercial point of view this made a lot of sense. If given a blank sheet of water I doubt that they would settle upon 125cc as the optimum capacity for a nongearbox two stroke kart engine.
Motocross again provides a useful insight. When four strokes were first introduced 250cc four strokes went up against 125cc two strokes. While the two strokes could match the four strokes peak horspower they were much peakier and consequently harder to ride. Riders en masse started to migrate to four strokes. When the first concerns began to appear about the extra costs associated with running four strokes, which was turning amateurs away from the sport, some governing authorities started to attempt to even up the playing field by relaxing the 2:1 capacity advantage of the four strokes.
Among the manufacturers KTM were perhaps the most active at trying to develop alternatives to the 125cc stroker. They first introduced the 144cc SX150 and a little later the 193cc SX200. The latter powerplant produced basically the same 35-37hp as the best 125cc two strokes and 250 fourstrokes, but because of its mild state of tune it basically matched the four strokes power right through the range. The 200 also weighed no more than the 125stroke, but was obviously much simpler, lighter and cheaper than a 250cc four stroke. A little later the rules were relaxed further in some Amateur competitions to let full fat 250cc two strokes race against 250cc four strokes, but these 250cc strokers, producing up to 49hp, are a real handful for all but the most talented riders.
Thus I believe a 175 or 200cc kart engine producing much the same horsepower as todays 125cc ( 30hp plus/minus a couple), revving as highly, weighing much the same as a 125, but having a much broader powerband would be a very satisfying unit to operate. Recently MotoriSeven appear to have embraced the idea of a 175cc kart engine (64mm bore x 54mm stroke) but I havent seen much in the way of specs or dyno curves to indicate whether they have used the extra 40% capacity to provide more peak power or a broader powerband or some combination in between.
Once again you are correct in stating that it shouldn’t be beyond the wit of man to devise a set of regulations that allow two strokes and four strokes to run together. In Dubai, Biland twins and Rotax Maxes competed for some time on a fairly even level running much the same weight. The Biland had a better bottom end and top end while the Max had a heftier midrange and ultimately more peak horsepower. It is likely that if they competed on a track with more slow corners and perhaps a longer straight.the advantage would have gone to the Biland.
Bilands were quite popular over here, but then they abruptly went out of production. The 34hp Vampire then arrived on the scene. Even with a 25kg odd weight disadvantage the Vampire proved too much for the Maxes and Iame X-30s. They just had too much power everywhere. However I understand in the UK you run them with carburator orifices so this would be one way of levelling the playing field. Quite a few people over here were interested in the Vampire engine, but then the relaibility problems started to surface and manufacture once again abruptly ended.
While I obviously think the simple carburated two stroke could be fairly simply updated to meet most realistic future emission targets as well providing an enhanced driving experience, it wouldn’t be all that surprising if 250cc four strokes do eventually become the dominant powerplant just as if they've done so in motorcycling. It slightly surprises me that one of the bike manufactuers , particularly those already with some exposure to karting ( Yamaha/ Honda) havent simply modified one of their MX or Enduro units for karting. Presumably it is simply the small size of the potential market that dissaudes them.
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The carbureted two stroke - the future of Karting by 'Max14' (13 Oct 2010 @ 6:11)
