Usually when I am rebuilding a cube carb I go ahead and install new lines and even a new pickup filter if I suspect water has been in the fuel tank. Die cast tend to corrode once exposed to water sending a grey mud thru the carb's internals. Many times the internal filter screen catches it but not always. There is also filter screen so tight on filtering they are clogged and not cleanable. These are the ones you can not see through in the first place.
Yes Tygon has its problems but sometimes that all that will fit in certain applications. Even though those lines claiming 100% Ethanol resistance are problem causers. I had one case on my personal saw where I installed new F-4040 lines and a week later the lines literally were melting in the fuel mix. I replaced with the same line (off the same roll) with the same fuel mix and didn't have any further problems. I can't to this day explain what caused the problem.
Stens came out with their Tru Blue line that claims 100% Ethanol but it fail internal tests here. Wasn't to harden or shrink which it did both. Harding leads to fuel pickup not moving around as it should and the shrinkage causing leakage at thru holes. Even the LP1200 line cause problems when its inner liner fails. It collapses causing fuel starvation.
Whenever I can I use Nitrile rubber lines which seems to superior to the plasticize lines as a replacement line but there fittings smaller than the 2.5 id line I have or in the case Poulan saws just too large OD to fit through the tank through holes. I am considering try to enlarge these pass through holes but just don't want to it on a customer before I get to try it on parts unit.
