Howdy,

I'm having problems on my .46 fx with air getting in the fuel lines. I have replaced all lines from clunk to carb with brand new in case they were old and had holes in them, no help. The line from the tank to the needle valve is clean with no air, but the line from the needle valve to the carb is where I'm seeing it. The more throttle I give it, the bigger the air bubbles get and the more erratic the engine speed gets. When I crank it up to full throttle, it really gets wild and then dies (presumably because the bubbles make it too lean). What are some other things I can do to isolate this problem?

Thanks!

Balance that prop!!!! This is the classic description of an unbalanced prop causing the fuel to foam. Had a guy at the field the other day with the same problem and same engine. Switching to a known balanced prop straightened it right up.

Sounds like your needle valve is sucking air past the threads , they say on here to put a short piece of fuel line over it & the threads. Do you see the bubbles when the tank is full? If you do it is hard to blame the prop , how can it foam with a full tank & the clunk on the bottom ? Besides you say you see no bubbles in the line from the tank to the needle valve. MAX H.

Yes, tank is full. And yes, no air bubbles from tank to needle valve. I has been about a year since I've started it up, perhaps I need to see if something in the needle valve has rotted (like the o-ring). When you say to put fuel line over it, do you mean to just stretch it over and on top of the whole needle valve screw/assembly?

Thanks!

Right , over the needle & the threads & piece maybe up to a 1/2" long. Probably could replace the "O" ring & cure your problem . MAX H.