Re: portable tanks and anti siphon valves
That is perfectly normal action and has nothing to do with an air leak or bad carb. You can prove this with a simple test. Fill clear tube, any size, with water put your finger over the end. Insert the other end of the tube into a pan, tub, or glass of water. Hold the end with your finger over it in the air. Air will make its way eventually into the tube and a "burp" will occur letting some fluid out. Wait a bit more and another "burp" will occur. That process repeats until the tube is empty. How quickly the tube empties depends on how big the burps are. The level of the tank in relation to the engine is only part of the issue. The fuel pickup is at the bottom of the tank so where it is in relation to other end of the fuel line is more important. In most cases the bottom of the fuel pickup is well below the level of the fuel line so gravity takes over -- burping the fuel out of the line. One thing folks tend to forget about is that even though you pressurize the fuel system with the primer bulb, the moment the engine starts fuel is drawn through the system so the system is no longer pressurized. Another misconception is that an anti-siphon valve prevents fuel from draining back to the tank. That is not it's purpose. It is inserted at outlet of built-in tanks to prevent fuel from siphoning OUT of the tank if there is rupture or leak in the fuel line. In most cases the fuel line from the tank drops below the fuel level on its way to the engine which is also mounted low in the boat. A leak anywhere between the tank and fuel pump will siphon fuel into the bilge. That is obviously not a good thing. Anti-siphon valves are not normally used on portable tanks because everything is exposed. That doesn't mean it's not a good idea to use one. It simply means that it has been deemed unnecessary for outboards using portable tanks. .
