This is really great info. I am thinking though, wouldn't outside ambient temp. have a big effect on this as well? If it is colder outside then the temp. in the exhaust will be cooler too, wouldn't it? Is it a safe assumption to say you may have to jet differently for summer and winter? I was thinking if the temp. outside is not close to the day you began your testing, would this throw off the results? Sorry I am fairly ignorant regarding this subject, but I'm learning.

 

Stebob, you are partially rightin that jetting is affected by temperature however your EGT reading is not directly affected by outside temperature. It is affected by this: Cooler air generally has a higher density than warm air. This means that on a cooler day your exhaust temp will actually be higher (jetting leaner) than on a warm day. Most trail riders will jet for the coldest conditions and lowest altitudes (higher density air) that they will encounter. That way they have a safety margin in warmer temps and higher altitudes and know they will not burn down an engine. Racers however will change jetting throughout the day depending on conditons to get maximum performance all the time. Hope this helps you out!