mainly just to let you know if you have a problem coming on, such as injector failure, etc. or getting too hot near redline. It'll let you catch it in time and take corrective action before you have a nice hole in the piston or something.
Oh, and timing has nothing to do with mixture other than more or less efficient use of fuel air combination. It's just not that simple, there are so many factors.
Ok but just for info purposes at this point, where should the egt's be at idle & then at say 3000 rpm's? A friend advised me that at idle it should be at about 900 degrees while mine is at about 700 so is that correct and if so why would mine be 200 degrees less than standard temp?
An egt for tuning is useless, unless you're tuning your ignition timing. Otherwise, its not going to do a whole lot for you.
For fuel tuning, you MUST go with a wideband oxygen sensor and controler module from FJO or whoever.
As mrd40z stated, timing is independ of fuel mixture.
Here's how this works.
Lean mixtures will produce knock. The knock sensors pick this up, and retard the timing to save the motor from burning holes in pistons, or cracking rings lands or what not. When this timing is pulled, the point at which energy (heat) is released is changed.
It still takes 5 milliseconds (just an arbitrary time i have no idea of this actual time) for complete combustion to happen. The only thing you can change is when you ignite it. We'll say that at 3ms into combustion, the maximium amount of energy (heat) is released. Idealy, we'd want this to happen just as the crank throw is about 15° ATDC (from memory) which would exert the most amount of force upon the crank.
When we retard (or pull) the timing, we release this energy later and later in the cycle. So late that some of this heat gets out of the combustion chamber and into the manifold. When this happens, EGT's go up.