Is the tank under pressure when you shut it down?

My guess is no.

If the tank was holding pressure then there is no way for the fuel to go toward the tank in that line.

Your plumbing is not correct or the tank is not holding pressure (has a leak).


From the symptom I would say right off hand your check valve is not installed correctly...the proper direction is to allow air from engine to the tank, and block the air from coming out of the tank.

Next thing is are you using a YS check valve. There are other varieties on the market that use a small ball bearing and a little spring. These take more pressure to close off. So when the tank is not up to pressue it will take longer to get up to pressure.

Next is to fill the tank with fuel, then plug up the check valve side and pump more fuel into the tank. This will build pressure in the tank. See if its leaking? It could be leaking past the check valve even though the check valve is installed with the proper direction. Check this. If the tank system will not hold pressure then it will not work.

The engine does NOT suck any fuel above 2000-2500rpm. It is force fed fuel above 2000-2500rpm by the pressure in the tank. The way it works is the tank is under about 6-8psi. The carb gives a little suck on the regulator and the plunger opens allowing fuel to flow past it as its under pressure. When the pressur ein the line gets to equal the pressure in the tank the fuel stops flowing and the spring will close the plunger. The only line that has any suction at all is the line from the Regulator to the Carb. This only happens when it is at the right spot in the rotation cycle and it is just a lower pressure than the 8psi in the tank. I doubt it is ever negative pressure...The enigne never really sucks fuel at all.

Now if the check valve is installed backward, or missing then the fuel in the pressure line will move toward the engines when its not on its pressure push cycle, and the when the pressure line is pushing pressure into the tank the check valve will stop it from going to the tank and act like the tank is already up to pressure.


Another option is the check vlave could be sticking from gummed up fuel and oil. You can pump raw fuel through them and this will usually un-stick a gummed up one.

Troy Newman
Team YS