oil mixtures

try leaning out your jetting before you lean out your oil check out the other topic regarding this there is a lot of discussion and websites regarding this
 
ya ok there not fouling out like all the time just like once in awile so i guss that is normal but i run really good so i will probily just leave it than
 
depends on how offen your fouling plugs, and riding style, if you putting around alot, and alot of lower rpm riding it will foul faster, my black blaster got over 25 hours per plug, but i spent ALOT of time jetting and fine tuning the carb, and it was as perfect as a stock yamaha carb can get, BUT like i said ALOT of jetting and tuning,

and a clean burn oil helps, if your running lower quality oil you will foul plugs more offen, i run pro honda hp2, its a clean burn oil, designed for honda cr motors, to help prevent port port( power valves) from getting gummed up,

now.. my old 84 honda atc 250r i ran honda gn2 2 stroke oil, which is a non synth/ none clean burn, and properly jetted and tuned i would foul a plug ever 6-8 hours of riding,
 
me and my bro went trail ridin. he has a yz80 and put in a new plug before we went and he fouled it within like 2 hours. mine seems to be great. i never fouled a plug yet but i change it every once in a while. and i always carry a spare one.