Working with the original tanks even if steam cleaned to the point that you think are clean there always seens to be some residual in the tank that causes problems. A full tank will have less problems than a 1/2 tank of gas. The 1/2 tank will slosh around more and get dirt in the line. I appear to have finally solved this by installing a perma-cool water/gas filter under the tank on the inside of the frame. Supposed to be a 2 micron filter and the filter has a water drain on the bottom. The cheapest place I have found them in in the Whitney Catalogue. They come with mountng brackets & Hoses. I did have to get some brass fittings to finish up. Make sure you put some thread sealer on the fittings & don't use the thread tape.

"Drugs are money, money is power, power is security." - Kent Heiner
Nedrow population 2212
Carbon footprint family of 2/11 tonnes of CO2/yr