The exhaust emissions from a single-cylinder spark ignition engine were measured as a function of burning time. Flame propagation time was measured with an ionization probe, and the exhaust gas was sampled with a gas sampling valve. Electronic control logic determined the cycles to be sampled, based on the flame propagation time. Tests were carried out at full throttle, for lean, optimum, and rich A/F. The exhaust components measured were CO, HC, O2, H2, and N2 using a gas chromatograph.The emission most affected by CBCV is CO. Cycles that are either faster or slower than the mean cycle have increased CO, particularly at lean A/F where a five-fold difference in CO concentration was measured. HC emissions show a 150% change for the same conditions. For other than lean A/F operation, H2 was an exhaust product, up to 6% at rich A/F operation.It is well established that reductions in CBCV would improve efficiency and power output. Here it is established that a reduction in CBCV would also reduce overall CO and HC emissions, particularly for very lean operation.