Starting Used Saws
I just finished a project where I managed to get two saws running and the third one was mine. First things first clean, clean, the hell out of it clean saw is easier to work on then a dirty one. The next thing I like to do is dump a cap of fuel into the spark plug hole, and crank on it if it fires then you can fix it if not change the plug and try again, if it still don't fire, then check the switch and see if it is working accordingly. I pull the wire off the switch, fill the spark plug and crank if the saw fires the switch is bad, if It don't you need to look at the coil, usually if I have to go passed the coil I try to consider the value of the saw,as sending units aren't easy to find and are usually quit expensive, so unless you have a parts saw or can get a good deal on the ignition think about it.
The next would be checking the fuel delivery, I have watched guys rebuild,and replace their carberator. Only to find out that a hole in the fuel line was causing the problem. I figure fuel lines are cheap and if The saw has set dry or otherwise, replace them I have never replaced a fuel line that I was sorry about. Seriously I have had saws that would start but wouldn't quite catch, or would catch but not tun in right surgeing stalling Ect.
My next move is to pull the Carb apart and blow it out with air making sure all passages are clear, and the gaskets and diaphram are in good shape
the diaphram is tough I have inspected them and tried to run them only fo find out that they had a small hole in them. Usually you can If you are careful you can disassemble blow them clean and put them back together, at this point though I might point out that it would be a good time to kit the carb.
If there were a secret that I almost hate giving up it is this, pull the muffler and make sure all the screens are clean. While you got the muffler off look at the exhaust port Alot of times there is carbon build up around the port. I usually roll the piston and ring line passed the port so the skirt is completely in the port window and then take out the old pocket knife and scrap the carbon away, then blow the port clean. I have got some good deals on saws because of this.
I ain't rich so A lot of the saws that I get to run are used, I can't make money with a saw if it don't run. I also don't have all the answers just a few some old timers taught me when I was A kid. So hope I helped, good luck.