When using an exhaust gas analyzer, your primary concern is the CO reading. Carbon Monoxide is the result and by product of the combustion. It is also the ONLY thing you can directly adjust. All other outputs and readings are a result of this. Hydro Carbons, or HC is the unburned fuel. The readings you get for HC tell you the efficiency of the engine for one. The lower the HC, the more percentage of fuel you are burning. All readings other than CO are used to determine what the problems are if they do exist. For example, if you have a very low CO output and very high HC, you are not burning very much fuel and dumping it out the exhaust as raw gas. This would tend to indicate that the engine, or cylinder if it is a multicylinder engine, is in a lean misfire. There is a point where there is not enough gas in the fuel mixture to burn, and it produces these results. The additional gas readings picked up by a 4 gas analyzer are Carbon Dioxide and free oxygen. Again, these are by products of combustion and are used to further determine where a problem could be. Personally, I generally like to see the CO set in the 3% to 4% range. I remember seeing Nick recommend 2%. I think it is a bit lean, and is below any specs I recall that Yamaha produces for its machines. Normally if you adjust your CO by watching your HC drop and achieve the lowest possible HC readings, you will have a fine running machine. CO is measured as a percentage of gas present in the mixture, HC's are measured in Parts Per Million. CO2 should normally be around 1% and O2 should normally be around 10%. As you can imagine there is a whole host of combinations that could show up when a problem exists. EGA's are useful diagnostic tools to help repair and maintain proper running engines. In an engine that wont start, you can still analyze the exhaust. If you get excessive HC, like more than 2000 PPM, you know you are getting fuel and must have an ignition problem, USUALLY. Conversely, if you are not getting any HC output, you are not getting fuel into the cylinders and would want to look towards the fuel system as the source of the problem. One other nifty trick with the EGA is sampling the oil in the crankcase to determine if it has been contaminated with gas. Now being GTS owners we should never have to worry about this on GTS's because they are fuel injected, but on carbureted bikes this applies. Sample the fumes in the crankcase for the presence of HC while the oil is cold. This tells you if there is gas present in the oil. This test only works on cold oil. Once the oil is heated up, all petroleum based oils will emit HC readings. RSRBOB
