Thanks Kodiak42 for the info. I guess I'll buy one and see what happens. And mountainlake, I'll be sure to richen up the mix before I put too much time on it.
Good luck Sapo, maybe you can get a deal on one. If you find a used one on ebay make sure they have pics of the cylinder and piston, you dont wont anything thats all scored up.
Another thing along with carb adjustments that can really heat the saw up is a dull chain. I've seen some pretty good saws get burnt up or seized by someone that was either too lazy or not smart enough to run a file on the chain, or just change it out with a sharp one. Brand name not with standing.
**Edit**
I just looked at the pics you provided, missed them some how until now, but on the cs 680 at least I would say the deflector was put on wrong and directing the exhaust back to the hand brake, that would make the melting make more sense in that area. I have ran saw this hard before carb adjustment and after with no issues, but I can gaurentee if put the deflector on wrong it would look like that pretty quick. The 680 muffler is setup to make the directional issue implausble if you try using all the bolts for the deflector (minus a couple and it can happen), not sure about the 670. But from what the saw looks like in the the pics the deflector was on wrong, in general overheating you would expect the plastic to be melted above the muffler also which it isnt shown on either pic that I can see, which is odd since its just less than a 1/4" above the muffler and the melted area is a good distance away, at least 5" in the direction of the exhaust blast if the baffle was installed wrong .
Looking at the pics, I'm 200% sure the baffles were on wrong. The Muffler baffle is located on the bar side of the muffler on this model and directs the exhaust at angle across the bar, in reverse it's back at the brake.
After further review the 670 only has two bolts holding the baffle on a flat stamp sheet metal muffler that looks fully interchangeable in terms of placement and appears to be fully revesible, the 680 baffle has 4 bolts (at least mine) with raised sheet metal from the muffler in the baffle area that follows the outline of the baffle and is not reversible without the exclusion of all but one bolt and an ill fitting baffle plate.
