Think I'd open the acetylene bottle a little more as well. Yeah it's low pressure & you don't need to (and shouldn't) have it open very far so it's fast & easy to close if needed, but 1/2 turn may not be cutting it.
I'd go 1.5 turns just to take that out of the equation. Also, with gear sitting around for 20 years it may have connected enough dust to screw with stuff.
I asked about your torch setup b/c of the upper/lower O2 comment & then you don't say anything about adjusting the O2 for your preheat flame after the torch is lit.
Just want to confirm that you're hung up on the acetylene issue & didn't mention that you then adjusted the O2 for your preheat. (B/c you def need to do that!
)
This is a halfway decent vid that shows the different preheat flames.
Give me a little bit & I'll upload a welding handbook that includes some in depth & practical oxy-fuel cutting info.
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