I would start by taking the engine covers off and check for fuel leaks. Get someone to squeeze the primer bulb whilst looking out for any leaks.
If there are no leaks then make sure you can read fuel data on the gauge accurately so you can assess the full extent of the problem.
To actually be burning that much fuel you would notice the engine running pretty poorly also the propeller would be full of black soot.
Worst case scenario is you have a leak in the tank possibly only happens when it is brimmed as the leak could be near the top. I assume you have a drain plug at the back so you can check to see if there is any fuel in the hull or if you can smell petrol in the hull.
I had a Honda 225 that had a fuel leak. This was after a service and the tossers that serviced it had not tightened the top of the high pressure fuel filter properly all the screws were finger tight.
Very difficult to see this until the side covers were off the engine. If the Suzuki has a fuel pump that cycles when you switch the ignition on then get someone to cycle the pump a few times whilst looking for leaks...
This is how I got it back fro the dealer...