I can't keep my Poulan pro 260 chainsaw running!!?

My chainsaw is 3 years old and not used much. Tried starting it after few months from last use and started ok. Tried next day and again it started but will not stay running. Changed spark plug and new fuel/oil mix, same thing. I noticed that the spark is not intense. I can hold on to high tension lead and just get small tingle at times. I checked the gap for the magneto with thin label tag but not sure what it should be. Same results. It seems to be getting fuel ok. The ohms reading on the high tension lead to ground is around 2500 ohms. Not sure what it should be. Will start at times and run at full throttle and then when I let off on throttle it stops and then will not start right away or not at all.If I pull plug out it is fouled and I blow it off with compressed air and sometimes it will go but with the same end results. Can you help me out??