Well I have read all the replies and they covered just about everything. The only thing I can think of that wasn't mentioned is if this is an old tank with the old plumbing that could be it. Now to clarify,you said; you changed all the lines by that I will assume the plastic fuel lines. Well bet the old brass tubing is still there, right? If so that can get pin holes from the nitro in fuel. Just a thought. Might be worth putting new in. Hope something works.