I've had several 36 and 41 saws and they all suffer from this issue when I "inherit" them. As someone else posted, the problem is the rubber intake sleeve and the rubber impulse tube seal. When you replace these two pieces use a little bit of high temperature silicone gasket seal on them. This will give a foolproof seal and make these parts last much longer. They are great little saws once you get them running correctly.
Another common problem with these saws is the muffler bolts. The muffler bolts vibrate loose and the screw threads in the cylinder strip out as a result. As well, the loose muffler will melt the plastic cylinder cover and saw chassis. This isn't easy to prevent because Lock-tite releases when exposed to high temperatures. My method is to drill the heads of the muffler bolts and install safety wire which ties the two blots together so they can't turn.
Steve
