Be sure to use the right alloy welding rod- - - -a soft metal rod that's easy to weld with will wear quickly and put lots of abrasive metal particles into the oil. You might want to consider using "hard facing" rod like the kind that's used to weld up the cutting edges of bush hog blades, etc. Once it's applied and allowed to air cool, it's too hard to file- - - -smooth it with an angle grinder. I'd strongly recommend finding the real cause of the problem, not trying shade tree fixes. Temporarily, why not just use an electric pump to get the engine running, then deal with whatever is keeping the mechanical pump from working?
Jerry
