Oxy-fuel welding help.
What Zout said. Not totally sure what your problem is, sounds like improper O2/Fuel mix.
Start flame with pure Acetylene, whispy yellow flame which smokes and sends out black soot..
**Add more fuel 'till soot goes and you get the inch of straight orange flame.
Slowly add Oxygen until blue flame forms then focuses. Keep adding O2 untill bright blue flame comes back towards tip but** does not leave the tip - gap between tip and start of blue flame.
Add some more fuel if greater heat is needed, each time increase O2 slowly to get the blue flame back to the tip.
Too much O2 will make the flame roar as it is about to blow itself out.... Which is the propper and safe way to extinguish the flame - blow it out with too much O2 before shutting off fuel. Stops pure fuel flame goingback up hose to tank!
When welding, the trick is getting all parts the same temp at the point they start to turn glassy, then liquid - which is the weld puddle forming.
If the two parts are discimilar thickness, warm the thicker first, occasionally heating the thinner, bring in the filler rod, also thin, get thet warm too, again - in and out of the flame (not the blue part) 'till it goes orange too. Try to drop the ball of filler rod melt, onto the work pieces, rather than keeping the end of the rod in the weld pool. Keep backing off the flame away from the weld pool as the puddle forms. "Push" the weld pool along the weld to join previous tacks. The phrase "chasing the onion" is related to weld pool control and advance along the joint. (Even a Trivial Persuit, or Battle of the Sexes board game question!)
This is one of the hardest types of welding to master - practise techniques for controling the heat to different parts by the proximity of flame and time in flame.
Hope this gets you further along - keep us all posted, I'm sure there are many welders on this site who, between us, will get you there!