This is what it was like when I got mine. It was clogged with dirt under the air filter, and it had been left with fuel in the tank for probably close to 20 years. It did fire up, but stopped immediately. Since it actually runs your spark must be there. What I did was to thorougly clean up the area under the air filter. Next I took off the carb. Everything is fastened with the two screws on the top. Then I took the carburetor all apart, and cleaned it, and all the bits in it with CRC metal cleaning spray. Remember to count the turns on the jets by turning them in lightly, before you take them out. You will probably need to adjust them again, but it will give you an idea of what the previous owner did. If they ran it rich it is good. After cleaning everything I put it back together the same way it was, and installed the carb back on the saw. And it started on the second or third pull. After a bit of tinkering with the low and idle screw it ran beautifully. Still does.
Edit: On high RPM the engine was failing a little bit, like losing fuel, and I could not adjust the issue away. After investing in a tune up kit with air filter, petrol filter and new spark plug, this problem is gone.