I just recently started adding castor oil to my fuel as well.....
the big difference in car/buggy fuel and airplane fuel is the oil content...Omega 15% is something like 18% oil
oil serves 2 purposes lubrication of course but it also carries away heat.....to cool a model engine you either have to increase airflow over the engine, or richen the mixture...
When you tune the engine never set it for max RPM on the ground..instead richen the mixture 1/8 to a 1/4 turn to rich from max RPM as the engine will lean out in flight...
bubbles in the fuel lines means a leaner mixture as well...when you replaced the fuel lines did you replace the lines inside the tank?
Is the fuel tank isolated from the airframe with foam...this lessens vibration to the fuel....lastly the high end needle could be leaking a little...in that case a little heat shrink around the knob to stop a leak, but that would be the last thing to try
good luck