In a message dated 9/26/00 6:00:57 AM Eastern Daylight Time, [EMAIL PROTECTED] writes: << Sounds exactly like my bike. As I said, I did a quick test on an exhaust gas analyser which seemed to show (apart from the poisoned cat) very high hydrocarbons at idle (hence smell of petrol/gasoline); >> An engine can show high hydrocarbons for several reasons. Hydrocarbons or HC for short, are unburned gas coming out the exhaust. Burned gas, as a result of combustion, is read as CO or Carbon Monoxide. You cannot properly interpret hi HC readings without knowing what your CO is. An engine can be so lean, it cannot burn the fuel it is getting, and thus produce hi HC from running the fuel straight through the engine. An engine running in this condition is called being in a lean misfire. If it were a single cylinder engine, it probably would not run, depending on the severity of the leanness. An engine that is too rich, obviously, can give hi HC readings because there is so much gas the engine cannot combust it. Therefore, to be able to decide whether you are rich or lean depends on going to the CO reading to interpret your HC reading. CO should be somewhere around 3 or 4 percent. If the CO is higher than that, the engine is rich. If the CO is lower than that, the engine is lean. Adjustments should be made accordingly. EGA adjustments should always be coupled with engine sync and engine idle speed monitored. If adjusted the mixture affects the sync or idle speed, they should be brought back to specs before proceeding with further EGA adjustments. A typical EGA adjustment is a constant adjusting of mixture, idle sync, mixture idle sync, etc. One other point, Yamaha specifies that the engine oil temp should be between 55 and 55 degrees Celsius when making EGA adjustments, with the crankcase breather unplugged. Gas in the oil can also show a high HC reading, without affecting CO. Obviously, there is a bit of experience required to be able to accurately interpret what an EGA machine is telling you, but that does not negate its value as a diagnostic tool. It removes all the guess work and allows for extremely accurate adjustments.
