The 4218 is stratto carb versus the 220 isnt.
Either way, they are both pretty much bottom shelf saws with the Poulan brand not being anywhere near the quality they once were pre Electrolux involvement.
Lots of things restrict these wee box store saws- lean from the get go, very cheaply made, dubious build quality and restrictive EPA type fittings- like choked up mufflers and restricted carbs.
Things can be "done" to make them run a little better- but at the end of the day, they are what they are and for the money if they are running on any given day- they will put wood on the trailer for you.
If I was in the States and looking to buy a brand new consumer saw, I would be looking at options from Echo long before Poulan.