If I can say something here, the black plastic "idle screw", is actually the throttle stop for wide open throttle. I always screw these fully in on re-assembly, and adjust them later with the engine under FULL load. Having them too far out can allow the engine to over rev, possibly causing engine failure.
And a tip for MIG welding alloy.
Reverse the polarity of the welder. This encourages impurities in the alloy to be brought to the surface, and for preparation, thoroughly wash the area to be welded with methylated spirits to remove oxidisation, and then do not touch it with bare hands.
