If you are blowing out on the acetylene your regulator should be
turned down as you have to much pressure set on the on the regulator,
you should just hear the gas coming out of the tip when adjusting
your regulator, and it should be a loud hiss.
If you are getting black smoke when using your # 4 tip, most likely
the tip is not getting enough oxygen, check to see if you are getting
enough oxygen through the oxygen nozzle and hose. To do this simply
hold the nozzle to your ear, if not enough oxygen is coming out it
could be the regulator, you would only have to buy the one regulator.
Have a good day.