ChrisK-RCU

I have an old (14 years) Fox .40 that I can't get to run properly.
It was rebuilt by Fox about 5 years ago, and the engine ran fine the last time I regularly used it (about a year and a half ago).
It will start and idle fine, and will run pretty well at high end too. However, It will only sputter and die at middle range throttle settings. What really confuses me is that I can see air being drawn through the fuel line into the carb at full throttle.
I have checked and rechecked the fuel tank and replaced the lines and I am confident there is no air leak. How could air possibly be getting into the system??? I have also put in a new glow plug with no luck. One problem might be that I am using fuel that I have had since last fall, but my other engines
run fine using this fuel.

I would really appreciate it if anybody has any ideas what is going on.

Thanks

GBR2

My Feedback: (1)

Despite your checking the tank and replacing the lines, the fact that you see bubbles means you have a leak or the fuel is foaming so much the bubbles are getting drawn in. I'd suggest taking it out of the plane and putting it on a test stand where you can have more controlled conditions.