Checking for fuel leaks

Typically when I check a integral tanked Cox engine for leaks, I close the needle all the way down. If you have the two vent backplate, this is easier than the single with the tiny vent air hole. Place your finger over one of the vents while using a syringe to pump air into the other vent. Small drops of oil on the backplate screws and also around the perimeter of the tank will quickly reveal air bubbles. In addition, listen and lend your ear to the rear venturi intake. If you hear air leaking directly out of the rear of the screen the o-ring is leaking. The syringe plunger is pushed down as if your trying to blow the engine up. The syringe shouldn't leak down at all. Most of the time, fuel is leaking from the screws themselves. In that case, my only recommendation is to replace them as this typically seals them back up. Bernie provides better stainless screws than the plated screws that came stock. I haven't found a sealer that really works well for the leaking screws and I have found many plastic and also metal tank backs that have had casting flaws and cracks. Ken