Once you can consistently recognize a welding heat the prime
success factor usually is the fuel. Metallurgical, high BTU, Low
sulfur, low ash coal really is makes a difference. A pure coke or
charcoal fire makes things even easier. Whatever you are using, start
with a brand new clean fire. Clear you firepot of all the dregs. keep
the fire tight not hollow. With welds that really matter I would always
make a few buckets of coke first and use that exclusively for my fire.
Try to do all your welding first thing before the fire gets dirtied up
with clinker and ash. Results will definitely improve.