I just finished cleaning and RTV'ing a couple of old engines (Airplane ProMagnum ABC .45 and OS .21 VF-BR buggy). I RTV'd crankshaft, back plate, carb base, and exhaust/muffler. I used no paper gaskets. Instead I used Permatex Ultra Copper High Temp as suggested in this forum.

To test the quality of the seals, I plugged the exhaust port and the carb, closed the needle valve completely, and use a fuel hose attached to the muffler pressure fitting to blow air into the engine.

My muffler is completely sealed as there is no leakage when the piston is covering the exhaust port.

Lowering the piston allows air to flow into the crankcase and out of the open carb. When I close the carb with my thumb there is still a small amount of air leaking. It sounds like it comes from the throttle barrel (carb was also RTV'ed). Is it normal for the throttle barrel to leak? Or should I have NO air leakage? Maybe its the mixing valve?

How can I test to make sure that the RTV seals are properly sealing?

Thanks.

Albert