more welding questions

[Porkchop]

I posted a while ago about oxy-acetylene welding. I have tried this welding since then. I am having some trouble with it though. I am using a book as an aid but it discusses mainly welding of thicker metals. I set the both the oxygen and the acetylene at about 4 psi and I get a good looking neutral flame (yellow outside and sharp inner blue flame). I can make a puddle but then it will just melt away and leave a whole. So I started using filler metal but my welds are coming out uneven between the two pieces of metal. I have been using a #1 tip which is .040", should I try a smaller tip? About how long should I expect to spend welding about 4". Does anyone have any advice for me, I am open to any suggestions. Right now I am working on patch panels on the body but will have to do all of the cab supports and some of the floor also - do you guys think that this welding will be strong enough for those jobs. Thanks for any of the help.
brad