I am getting bubbles in my fuel line between needle and carb, the fuel tank line is bubble free-I have read somewhere about needle problems-both of these needles are metal units on the backplates of engines any ideas-both of these engines have been running correctly until recently and now run lean and die-, I have replaced the fuel line between the carb and needle as well as tighten all fittings and needle valve holder=thanks for any ideas

If the engines have been running well for a while and then start to have problems, you need to do some detective work. It may be leaky needle assemblies, it could be a pinhole in the fuel line that allows small leaking and then the air bubble become visible after accumulating at the needle.

im having the air bubble problem too with the os 61 fx with the remote needle valve , air appears only in the line between the needle vave and carburetor, replaced fuel tank all fuel lines , and even a new back plate w/ needle vave, same problem , unreliable engine keeps stalling .I have also heard of the same problem with the .046 os engine with remote needle valve.

You will have to check to see if the needle valve assembly is leaking air at the fuel nipples or through the needle. Sometimes, the small teflon gaskets on the fuel nipples of the needle valve assembly are misshaped and allow air leakage. If so, they need to be replaced.

i replaced the entire back plate which included a new needle valve and seals, i ran the motor and had no bubbles between the needle and carb for about two minutes , then they came back when the engine warmed up. I gave up and bought a new os 75 ax because the needle is in the carb and it has no backplate to transfer heat to the fuel .I wanted a little more power for my plane anyway , its almost like the fx motor vapor locks.thank you for the info.