I have an air pump on my speedster mounted on the side of the drivers side seat assembly. It is connected to the gas tank and a pressure gauge through 3/8" tubing. The gas tank cap has a valve to allow either gravity feed or pressurized.
I have never actually needed it but always thought it looked "right" on the car. But here's the rub. It has never worked. I put a new leather on the bottom of the rod, but pushing it only blows air out a very small threaded hole on the bottom of the cylinder near the main outlet. If I put a screw in the cylinder you can't pul the plunger as there is a vacuum.
So, obviously there should be a check valve there in that hole. But the hole is so small I can't imagine how one fits. Anyone have a similar pump or know where I can find a very, very tiny check valve?
If you can find a way to hide it, the vendors sell an in-line check valve for tire pumps:
Your problem intrigues me;
1. Can you blow through the tube from the pump to the tank? Air should flow freely towards the tank and there should be a check valve to prevent it flowing from the tank to the pump. Maybe there is a blockage or a check valve already installed backwards??
Fixed it. There was a very small threaded hole at the cast base on the bottom. But it was way too small for a check valve. So, I went to an air compressor shop and bought a small brass check valve with. 1/2 " pipe thread. Then drilled a hole on the base and threaded it for the valve. Filled the small hole with a screw. Now it works.