Hi, My dad has an older BG85 and it starts by the 3rd pull, idles fine, revs fine but when at WOT, it seems like it goes to full throttle for a few secs (sounds great) then it slightly revs down or maybe you could call it a slight bog. I have tried many different types of canned 50:1 mix, changed the plug, air filter, fuel filter and cleaned the exhaust screen. If you think it maybe a carb issue how would someone go about rebuilding one on a Stihl? I mean where do you get parts manual or service to reassemble the carb? I'm trying to learn about 2 cycle engines but scared to take carb apart without some sort of reference. It's almost twenty years old anyway, so I really don't want to throw a lot of money at it. Thanks!