I have been trying to tune my os 37 for a long time now. It keeps losing power like I can't keep it up high because after awhile it will fall from slow to fast power lose. I have tried tuning leaning in and out both high and low niddle. I also checked fuel lines and tank. It seems to me to be running lean but sometimes when I go to move it alot of fuel poors out of the muffler. So I leaned it out a good few times and tryed riching it up trying everything for weeks now and can't get it to run right. I also noticed lately it has had like darker fuel coming out of muffler like greenish brown latest was black whats that mean? I need help please any ideas? I think my engine maybe finally broke in since not that old so can see why I might need to tune but tryed everything on needled many time please help.