if the op's saw has the easy start or simpull or whatever poulan calls it, order the non easy start version. the inner pulley, spring and outer cog get crammed full of dirt and dust, the spring stretches and elongates and will usualy get caught on that black sleeve the flywheel bolt holds against the flywheel. that sleeve or 'collar' is there to support the pull start pulley so it won't flop around when starting the saw. get the regular pulley, keep it clean and they don't have problems. some of them i changed, the customers even said the saw felt easier to pull over than the easy version.
another thing to look at, but will usually cause other issues, is the engine bolts. if they're loose, the engine isn't centered in the pullstart. it doesn't take much, but usually you'll have an untunable air leak.