Good poiints:
Pioneerguy600: I believe you have made some good poiints. As you say the older saws didn't rev as much, were less restricted, ran higher oil ratios and produced less heat and with a properly adjusted carb and no air leaks they ran cooler. My newest saw is a Poulan 3400 CAV. and she is totally original down to the spark plug and used very little. She calls for a 16/1 mix. of poulan oil. I now run full synthectic and run her at 32/1 mix. Originally she seemed to me to run hot, especially in the summer heat, even with the 16/1 mix and the carb adjusted as you say by ear. The muffler was way restricted. Muffler outlets were only 20% of the exhaust port area. I opened up the muffler to 80% of the exhaust port area and the saw ran much better. I also removed the spark arester screen and opened up the holes in the piece the screen was wrapped around. I also put a bit larger screen inside the muffler where I drilled holes to open her up in the front of the muffler. At 32/1 with a properly adjusted carb the saw breaths much better, runs cooler and runs like a totally different saw. About the only other improvement would be to change from 3/8" chipper chain to say a round ground/square ground chisel chain. As you say there are more newer saws with seal and bearing failure. I truely believe that runing a saw say at a 40/1 ratio with todays oils and slightly richer mixtures would greatly improve the life of the saw. Running a saw say at 50/1 or higher ratios and tuning the carb for the saws Max rpm range (leaning out the carb) only reduces the max life of the saw in my opinion. What you would gain in performance, would only reduced the saws life expectancy and cost more in repairs in the long run. A saw engine is air cooled, but more importantly is cooled by the vaoprized gas traveling through the crankcase. Lean out the mixture and use less oil and you will have more heat. Someone mentioned brown deposites, like a varnish, in thier saws crankcase. To me this only shows the saw was running at a hotter temperature and the fuel mixture was cooking to the sides etc of the crankcase and not properly lubricating and cooling the saw. There may be other opinions/arguements form others, more in the know than I, but these are my thoughts. These newer so called EPA carbs present a problelm, in that they are not adjustable, from what I can gather and alot of them are being replaced with adjustable carbs. In this case you are stuck wiht running the oil mix called for, cause adding more oil to the mix wll only lean out the air fuel mixtue and cause the saw to actually run leaner, so either opening up the carbs jets a bit or replacing them with larger ones, or puting on an adjustable carb is all your left with. You, in my opinion, can't open up the mufflers on these new saws without retuning the carb to a richer air/fuel mixture. There's not much that I can see you can do to these EPA saws without modifying the carb to compensate for any changes. The carbs usually are set on the lean side and any changes/mods will only make the saw run leaner. OK, not trying to write a book, but as said, some interesting thoughts and observations. Everyone take care. Lewis.