Actually on the jetworks website i believe the promote these for more rec riding application than racing.
"We designed the BlackJack Carburetor so that it could be used as a recreational model yet perform like a race only carburetor on the track. The requirements are quite different between a racer and a recreational rider.
The racer requires the maximum available air flow for the best top end speed possible. Most race craft leave the starting line between 2,500 to 4,000 rpm, usually with 2 holders holding the boat back. They have plenty of compression, lightweight flywheels, and relatively low pitched impellers to allow for the high rpm's needed to maximize the cylinder porting and pipe tuning requirements. This type of watercraft seldom needs to accelerate from a real idle speed.
The recreational - weekend rider requires instant response right from idle speed with frequent accelerations from idle to top speeds, and consistent response through turns. These type of watercraft usually run lower octane pump fuel and thus, lower compression. They also have heavier flywheels. This causes a longer dwell time relying on the low speed - transition circuit. This is the critical time because the air velocity through the carburetor is too low to start acting upon the high speed circuit. This is especially true when dealing with larger-than-stock carburetor bore diameters, let alone modified larger than stock-bore-diameter carburetors."
