Why Are 47cc Pocket Bikes More Powerful Than 49cc Pocket Bikes?

Paradoxical as it may sounds, 47cc pocket bikes tend to push out more powere because they are fitted with reed valve engines. The larger 49cc machines are usually powered by conventional piston skirt engines which, despite their larger cylinder capacity, can't hope to match the much more efficient reed valve.

The reed valve, or case reed inducted, engine scores on output because the carburettor sits on the crankcase, and fuel intake into the cylinder is via the transfer ports only. The reed valve is the mechanism by which the fuel/air mix is blocked from re-entering the carburettor.

The big advantage of reed valves over piston skirts is that a selection of reed valves enables an engine to be precisely tuned to  suit individual riders and tracks. A well-tuned race-prepared reed valve engine will leave a piston skirt motor for dead.

The 49cc piston skirt engine has the carburettor fitted directly onto the cylinder. Intake of fuel is governed jointly by the piston covering/uncovering the intake port and by induction through the transfer ports. When the piston stroke seals the intake port, the fuel/air mix is prevented from leaking back into the carburettor.