The aim of this study is to investigate the suitability of neat ethanol (95%) as an alternative fuel in an engine converted from diesel to ethanol, and experimentally determine the effect of different main fuel jets at carburetor on engine exhaust emissions and fuel consumption at high engine compression ratio (CR) of 14. For this purpose, three different diameter main fuel jets (1.40 mm, 1.50 mm, 1.60 mm) were used for ethanol fuel tests in a naturally aspirated four-stroke pre-chamber diesel engine. Tests were made at full-load conditions at speeds between 1200 and 2600 rpm at intervals of 400 rpm. In addition, cold-start system was developed and engine could be operated at reliable idle speed and medium speed down to 0 C ambient temperatures. The results show that HC emissions increase with increasing fuel jet diameter and CO, PM and HC emissions reduce significantly at idle speed and medium engine speeds. (C) 2009 International Energy Initiative. Published by Elsevier Inc. All rights reserved.