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Figuring out the problem
If you are an extremely experienced tuner, you can often tell the condition of your tuning by how the sled reacts. Example: If it is “doggy” on the top end, it is often too rich. If it is on the lean side, that’s a little tougher, because the sled will often run faster and you might be reluctant to change it. Unfortunately, that “seat of the pants” kind of experience is often based on a number of burn downs in the school of hard knocks.
A time-tested method has been to check the color of the spark plugs. If they are black and oily, then you are probably too rich. If they are coffee brown, then you are doing fine. If the plugs are ashy or white, then you are running on the edge of disaster.
However, there are several problems with reading plugs. First, it takes a while for them to color up, and if you put brand new ones in, they may still read light after a day’s running. Also, some of the new synthetic oils don’t color up well and may actually show ashier gray even if the mixture is good. There is, though, a pretty good solution that is also affordable and always gives you good information while you are actually riding under power. This little instrument is called an EGT meter.
EGT is short for Exhaust Gas Tempera-ture. By recording the temperature of the exhaust gases, you can tell what state of tuning your engine is in. A correct mixture will read around 1,150-1,200 F. Too lean a mixture will hit 1,300 F or more, and too rich will show around 1,000-1,100 F. EGT meters were originally developed for airplanes so the flight engineer could adjust the engines according to the outside temperature and pressures.