I flew my airplane this morning and had the engine quit on me twice with successful landings. I have a PT-40 with a OS LA 40 mounted to it. I noticed that the fuel line from the remote needle to the carb has developed bubbles, I have replaced all the fuel lines with new and lengthened the hose slightly from the carb to needle valve, as I suspected the cylinder heating the fuel line creating a little vapor lock. Still does the same thing, I am now suspecting the o-ring on the needle valve letting some air by. Has anyone had this problem and can one purchase an o-ring or is a whole new valve in order. I just installed the remote needle assy new from Tower about 3 months ago. Appreciate any input
-Tom

I'm certain you can get a new O-ring. Some people use a sort pice of fuel line over the needle valve that will get pinched between the needle and the body to stop air leaks.

Enjoy,

Jim

With a pressurized tank you will not usually get an air leak through the needle valve at full throttle. If you use a pressurized tank you need to make note of when you get the bubbles. If you get bubbles only when the engine is idling then it is from an air leak. If at high speed then it is from the pressure drop across the needle valve causing a small amount of the fuel to vaporize. If the latter you can loop the line above or below the needle valve to reduce the chance of the bubble getting to the engine, but usually if it does the engine will only have a quick burp and not.

If you don't use a pressurized tank then I recommend that you do.

Thanks for the input, I ran the engine twice more after I posted this thread. I found that the bubbles appear from idle to around 1/3 throttle. At W.O.T. it makes bubbles except they are almost unnoticeable. I do run a pressure tap off of the muffler. If I understand what you mean about looping the fuel line, I should use a longer piece of tubing between the carb and the needle and loop the excess?
-Thanks Tom

If they are almost unoticeable I wouln't worry about it. However the air leaking in at low speeds is another matter. You need to replace the O ring, or cover the end of the needle with tubing.

On re-reading the original text, I withdraw everything that I said before I edited this post. Sorry.