The 30-second answer: Most “fuel” problems are simply old gas or a gummed carb, so start there. If fuel truly is not reaching the carb, walk the system in order: gas in the tank, fuel valve open, filter not clogged, lines not cracked or kinked, and — on units with a fuel pump — the pump actually pumping. A can of fresh fuel and a few feet of line fix the large majority of these.
The fuel system on a portable generator is short and simple: tank, shutoff valve, filter, lines, sometimes a pump, then the carburetor. When the engine starves, the fault is somewhere along that path. I troubleshoot it the same way every time — tank to carb, cheapest checks first — and it rarely takes long.
Start with the fuel itself
Before blaming any part, look at the gas. Ethanol fuel goes stale in about a month and turns to varnish over a season. Old fuel is behind more “fuel system” complaints than every mechanical part combined. Drain it, refill with fresh, and try again. If the engine fires and runs on fresh gas, you were chasing stale fuel, not a broken component.
Check the shutoff valve and filter
Make sure the fuel valve (petcock) is fully open — it sounds obvious, but a half-turned valve starves the engine under load. Many generators have an inline or in-tank fuel filter; a clogged filter chokes flow. Pull the line at the carb, open the valve, and you should get a healthy gravity flow (on gravity-fed units). No flow or a weak dribble points to a plugged filter, a clogged valve screen, or debris in the tank.
Inspect the lines
Rubber fuel line hardens, cracks, and collapses with age. A cracked line lets air in (lean running, hard starting); a soft line can collapse under suction and starve the engine. Replace anything that looks brittle or weeping with fresh small-engine fuel line and new clamps. Check for kinks where the line routes around the frame, too.
Test the fuel pump (if equipped)
Larger and some inverter generators use a vacuum-pulse or electric fuel pump instead of gravity feed. To check a pulse pump, disconnect the outlet line, crank the engine, and watch for fuel pulsing out. Nothing coming through with good supply going in means the pump’s diaphragm has failed — a new pump is inexpensive and bolts in. On electric-pump units, confirm the pump clicks/hums when you switch on; a dead pump means no fuel.
The carburetor is the last and most common stop
If clean fuel is reaching the carb but the engine still will not run right, the carburetor jet is gummed. Pull the bowl, spray the main jet and passages with carb cleaner, and blow them out. A carb that is corroded inside or will not stay clean gets a rebuild kit or a replacement. For a step-by-step, see our guide on cleaning a generator carburetor.
Prevent the next fuel problem
Ninety percent of the fuel-system calls I see come back to one habit: leaving fuel sitting. Either run the carb dry before storage (shut the valve and let it stall), or treat every tank with a stabilizer. Do that one thing and you will skip most of the troubleshooting above for the life of the machine.