hi, i have a flt 26cc gasser. carb has one fuel line coming in to carb. and says there is no return. how do i run a ventline for the tank so it dont cause a vacum inside the tank. thanks for allyour help.

No, gas engines do not run a vent line like glow engines do. There is only one line going to carb for the fuel feed. The engine develops a vacuum that draws the fuel into the carb. The vent on the fuel tank needs to be vented outside of the fuselage.

Ken

Loop it over the tank and then just run it out below the fuselage. You can hide it in the cowl or other feature. In the image below the vent is to the lower right, fill in the center and manual kill switch to the left in the cowl's airway.

As RCKen said - gas engines have a diaphragm pump and don't need a return pressure line from the muffler.