I cant remember where but i read an article on two stroke fuel mixes and the article said that running too much oil can be as bad as not enough, The theory is that if you run too much oil the engine runs alot hotter and will burn or hole the piston etc.. personally i would run the reccomended mix, which for the 290 is 50:1 i think,
two of my friends have 290's and they both run at 50:1 without problems,