Originally Posted by shuttlebus
Just to add my tupence worth...
Rich mixture - burns with a yellowish flame (may be some traces of blue) - incomplete combustion. Will cause fouling of plugs, especially at low revs (and hence why it is a good reason to rev up a piston engine before TO to clear them). Deposits on plugs are black/sooty. Engine response after low speed running can be sluggish at best.
Ideal mixture - burns with a blue flame (reminiscent of the bunsen burners in school). If your mixture is correct a nice chocolate brown deposit ends up on the plugs!
Weak mixture - burns with a blue white or white colour. Hotter than ideal mixture. Plug deposits are a white & chalk like. Continued leam runnign leads to over-heating of the spark plug, thermal failure of the electrode and as mentioned above sharp detonation rather than a nice flame propogation, which can damage the engine.
Regards,
Shuttlebus
Your ideal is actually slightly on the rich side, this is also to aid cylinder head cooling by using the extra fuel to assist in it.........
When we set the idle mixture on a 152 or indeed any light aircraft we set it to run rich, this is easily seen next time you shut down.......... AT IDLE which will be about 650 rpm pull the mixture closed very slowly you will as the mixture leans (toward the optimum combustion ratio) see the RPM rise about 25 to 50 RPM this is because the engine has been set up on idle mixture to run slightly rich......... leaning it it is getting to the optimum so accelerates slightly before it dies...........
that is how we set it.