I've been an air conditioning, refrigeration tech for about 37 years and have never had this problem before. Got an MC tank refill last week, hooked up my 36 year old Prestolite assembly with the threaded type tips that I've always used and instead of getting my nice blue flame, I got this yellow flame with black soot. So I thought OK, I've got a clogged screen. I changed tips to one of my Robin-air double tips with a new screen in it-----same thing. I thought OK, Maybe its time to get a new kit, so I ordered a new one which looks identical to my Prestolite but instead has the name Uniweld. It even came with one new tip. Hooked it up and it too did the same thing. About now I'm going nuts. I took the MC tank back thinking I got bad gas. They asked me if I had it laying down---NO! Got another tank and it did the same thing....I am totally baffled and everyone I've talked to has no answers....HELP!