I have been working on a 1973 Crafstman 2.1 chainsaw, and just recently got it running. It runs ok, it just needs some fine tuning. I am not sure what to think about bubbles in the fuel line. When it is idling, they move a little bit. When you rev it up, the rush to the front of the line and stay right before the metal from the carb input fitting. As far as I can tell, they don't really affect anything but I am wondering if they will or if they are harmless. It's a good old saw, made in the USA and has 2 compression rings.