Welding needs some CO and other gases to make a good shield. If you have ever tried welding with a propane torch you will see it burns too clean to shield well (all you get is CO2 and water vapour)
I suspect the gasoline torch is similar, and makes porous, brittle welds much like the so called "Brown's Gas" welding torches. Browns gas is really just a form of hydrogen gas so it burns even cleaner and makes terrible welds.
If you do a google search, you will find the supporters of Browns gas, then you will find a group of people bilked out of thousands of dollars for non functioning machines that cost a fortune to operate! The guy selling them is quite a fraudster using rigged demos and tests.
For example he uses and IR temperature gun to say the flame is cool, only so many degrees then welds with it. Well, IR guns are calibrated for certain surfaces, and guess what, they read really low on hydrogen flames!
Ken