PROBLEM: Tank will not fill without constantly shutting off the nozzle or to fill the tank requires letting the fuel trickle into the tank from the nozzle.

The cause for a tank that has this problem is that the air and fumes escaping do not equal the amount of fuel being put into the tank. More fuel and less evacuation leads to pressure in the tank which will cause the ICV  to close and the fuel to back up to the nozzle and shut it off. There could be several reasons for this. Most of the points below have to do with managing the air flow in and out of the tank.

1. The canister is partially or fully clogged. See section farther below. During filling, remove the hose that runs from the tank to the canister (usually a 5/8” hose) and see if the shutoff issue goes away. If it does, further investigation is needed into the canister. Contact the canister manufacturer.
2. Hose from FLVV to canister and P trap is clogged. Remove and confirm hose is clear.
3. Hose (usually a 5/8” hose)  from FLVV/FLV to deck fill is clogged. Remove and confirm hose is clear. Hose could be routed to deck fill in a canister or pressure system.
4. Hose routing in boat is such that there is a low lying segment, low compared to the top of the tank, and it is in a location where fuel, if it were to get into it, could reside and cause a restriction of the flow of air through the fuel, with bubbles occasionally burping through, thus causing poor venting and intermittent filling stoppage. Move hose location to eliminate the low area.
5. Vents hoses could be kinked or pinched or have too tight a radius that restricts the inside diameter of the hose. Check all hoses and correct any issues.
6. Valve downstream from canister could be closed. Check to make sure that the p-trap that exits through the boat to the exterior of the boat is open.
7. FLVV/FLV is not working correctly and is closed off.
   1. If #1) above does not help the issue, it could be an FLVV/FLV although this is usually not the problem. We do not recommend that the FLVV/FLV be removed from the tank to be inspected. All of the tanks we produce are leak checked at 3 psi after the complete assembly to verify that all components are sound and that they do not leak. Removing the FLVV/FLV voids the factory test. Two options, then. Remove hose from FLVV/FLV that leads away from the component and during the fill operation, feel with your hand to see if air can be felt rushing out through the 5/8” opening of the component(s). To make it easier to feel, wet your hands with water before starting this. If you feel the rush, the unit should be working correctly and as the tank fills and the valve action is induced by the fuel, the air will stop. But, at that point the tank is full of fuel and could discharge on the person performing the test.
   2. An alternative, is to introduce air into the tank (3 – 5 psi) and again feel to make sure that the air is coming through the component(s). This test must be done when the tanks is less than full because at full, the FLVV/FLV should be closed.
8. Tank is tilted beyond what it should be and the FLVV/FLV is closing prematurely and causing shutoff, as it should. Tanks are engineered to work at certain angles to guarantee that they will fill and vent. Past these angles, there is no guarantee of this due to the simple hydraulic laws of nature. See the “Tank does not fill to level that seems full” section below. 
9. Fuel RVP (Reid vapor pressure). Winter mix of fuel having a higher RVP and being used when the weather gets warmer can produce higher vapor pressures and cause the ICV to close prematurely.
10. Warm fuel temperature. Warmer fuel can produce higher vapor pressures and cause the ICV to close prematurely.