Dual plug heads are of benefit more at high rpm, the dual ignition source enables higher compression ratios and higher rpm as the dual flame front promotes faster burn times and quicker cylinder pressure increases. The doubling in the number of spark plugs requires a similar doubling of ignition components otherwise the spark strength is halved if two plugs were sharing a coil.
Fitment of dual spark heads is increasingly common in over-square short stroke high performance engines to cope with the more accurate burn required in a high compression lean tuned modern engine. By the time a dual plug head is required on a 2 stroke, you are verging on pure race tuning - that is the engine will make a lot more power than stock, but become increasingly revvy and finicky about mixtures and atmospheric conditions. It will have marginal bottom end performance and a much shorter time between re-builds. Constant over-revving tends to be very hard on wrist and bottom end bearings, and unless you were competing at a high level it was really counter-productive for any casual use. Better to concentrate on rideplate, impellor and intake setup - which are the weaker points of those machines from stock, and having improved the grip and stability at speed of the machine perform relatively mild tuning to improve crispness and acceleration out of the hole, there is little point in trying to compete with half the size (or less) engine in a drag race with a modern PWC. The whole reason Kawasaki was so successful with the Jet-Ski models for so long, was it kept the machine simple and reliable, and even today the 300/440/550 series are very well liked and capable, with a huge following. Kawasaki is credited with creating the PWC market as we know it today, but times have moved on and the machines are quite different now.
