I picked up a Jonsered 670 champ. Seems to have poor compression. I dont plan to repair or rebuilt it myself but I'd like to get familiar with it and what's wrong before sending it in to my local guy. Novice curiousity. I've removed the two longer Allen key bolts that pass through the muffler, but the muffler does not want to come off. Is there something I'm missing that's still holding it on? Could it just be stuck on and need some pb blaster to get it separated? Many thanks.