for 1st attempt you have to hold white paper on one side of muffler, it gives you or clarify the colour of smoke, different colour indicate the health of engine, oil burn/consumption( piston ring not scrapping oil from liner wall),water in oil ( may chances of cylinder head gasket torn out, may be hair crack in liner) fuel injector dribbling or not calibrated or time to calibrate, choke air cleaner etc. etc.