AMSOIL is the best according to the stats and i use 20/50 but i live in Fl. i guess it would depend on temps where you live, hot temps i think would call for 20/50 but cooler might be a little better with 10/40?? or 15/?? so its ok to run other than specified oil to mfg recommendations, thats what it is recommendation, it just veries as to where you live. when i lived in Mi. i run 10/30 in the winter and a little heavier in the summer but that was back then and i was useing standard oil not syn. hope this helps but i am sure others will chime in and there is a whole section about oil in the archives somewhere, because there have been soooo many ask this question.
