When you weld with a stick welder the carbon and residue from inside the pipe gets in the weld and causes porosity. When I think 2 stroke pipe I think 20 gauge, it can be done but you need to be a damn good stick welder to weld 20 gauge with a stick, then add the gunk inside, theres the problem.
Cheap fix, break out the oxy/acetylene torch and a brazing rod.
About the wrap and spray, have you priced the stuff out yet? It's an expensive waste of money.
I know, I know it's cheaper than replacing the pipe, but look down the road, cheap fix that doesn't work times say three = huge waste of time, frustration. Probably cheaper to replace it. Thats a guaranteed fix.