I have been trying to weld a loop on the butt (running line) end of a Royal Wulff Ambush fly line (8wt) without success. I am using the heat shrink tubing, and have tried different settings. The welds either burn (too hot) or look cold and fail. A good looking weld broke at the junction between the weld and the line with very little effort. I have had good success welding AirFlo and Gaelforce lines. Is there something unusual about the Ambush line?