The purpose of this study is to evaluate the effect of an exhaust throttle installed in an exhaust pipe in a two-stroke motorcycle engine. In the experimental study, the exhaust-throttle system prevented fresh-gas from short-circuiting and consequently, improved unburnt hydrocarbon emissions and fuel economy, along with enhancing combustion stability. In actual running, in order to minimize HC emission level and stabilize cycle-to-cycle fluctuation of combustion including intermittent misfiring, an air-induction system and a long-duration spark ignition were used in addition to the exhaust throttle system. The control software for the integrated system was also a key point in improving HC and CO emission levels in the ECE-40 operation cycle. For detecting misfiring in the ECE-40 cycle, time-resolved HC variation was measured by a fast-response gas analyzer.