<div class="htmlview paragraph">Single-cylinder experiments were conducted with a 3-valve carbureted pre-chamber stratified charge engine in comparison with a conventional engine. The pre-chamber engine operation is governed by many design and operating variables. This investigation was limited to determining the effect of overall air/fuel ratio, ignition timing and EGR on emissions and fuel economy at a single road load test condition.</div> <div class="htmlview paragraph">It was found that, as for the conventional engine, these operating variables are also significant for the pre-chamber engine and that a compromise must be made between good fuel economy and low emissions. The main virtue of the pre-chamber engine was found to be the ability to operate at leaner overall air-fuel ratio. This resulted in lower nitrogen oxide (NO) emissions than the conventional engine without EGR. The unburned hydrocarbons (HC) were found to be higher for the pre-chamber engine up to the conventional engine lean misfire A/F ratio.</div> <div class="htmlview paragraph">Exhaust gas introduced into the pre-chamber was found to reduce NO emissions significantly without a large corresponding increase in HC emissions as observed with the conventional engine.</div> <div class="htmlview paragraph">Only at very low NO emissions with severely with severely retarded spark timing and/or high EGR rate did the pre-chamber engine show a fuel economy advantage over the conventional engine.</div> <div class="htmlview paragraph">As the test program was limited to one load and speed, the results should not be construed to be typical of all modes of operation.</div>