Tank Sludge.

What I did when I ran into this problem was to drop the tank, get a gas tank sealer kit and do it yourself. Kit has a metal wash which desolves all the fuel varnish. Next is something called OXISOLV which will etch the metal. Next comes the sealer. Worked great. I bought it at a swap meet, but Eastwood has the kit. Kinda steep @ $44.95 but cheaper then a new tank. :thumblef:
Mac