I have a engine problem which has been bugging me for a few months. Hope someone can help.

The engine is an OS32Sx on a pattern plane, fitted with a tuned pipe. The engine starts normally,
tuned slightly rich, and throttle advance is smooth. However after taking off and flying for a minute or so,
it will suddenly cut off when the throttle is reduced. After landing deadstick, I checked the temperature
and I would say it's normal.

In spite of various combination of fuel mixture for high and low end, glow plugs, and even switching to
a second OS 32SX, the cut-off still happen! One thing is I noticed a lot of bubbles in the fuel line (at mid throttle)
between the high-end needle and the carb. One of two of the engine screws were also loose.

Could the bubbles cause this problem - cutting off when throttle is reduced?

Chris