POWER JETS FOR DUMMIES
The first thing to understand about power jets is that they’re badly named as when fitted they can actually reduce bhp very slightly, yet anyone with a tuned engine should consider fitting one. Why? Because they’d be better known as safety jets and add an extra dimension to keeping a tuned engine running well.
One thing that occupies more discussion on forums and in pubs across the country is jet-sizes as however well a carb may be set up its jetting is inevitably a compromise. This is why most modern vehicles are fitted with computer controlled fuel injection systems that are capable of instantly adjusting the fuel/air mixture as required.
Anyone who’s been around scooters for a while, particularly in pre dyno days, has at least been present when a piston has holed. Many have suffered it themselves and know the cost of putting things right. In almost all cases the piston failed because of an overly lean mixture. This may well be down to incorrect jetting but even the best prepared engine is at risk when the throttle is closed suddenly. For the short time it takes for engine braking to set in, the mixture is far too lean and particularly in tuned engines running at high rpm, it’s very possible for the burn temperature to reach a critical point with terminal results for the piston.
A power jet is a self-contained fuel feed that responds to a vacuum which is created when the throttle has been closed but the engine is demanding more fuel. Without increasing rpm, it creates a richer mixture, cooling the burn temperature until the vacuum settles and the mixture returns to normal – leaving the piston surviving to fight another day.