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I have a z520a that just cranks but won’t start. I’ve got a new battery, plugs (and they are sparking), fuel pump is working properly, air filter is clean, fuses are good. Is there a way to test if it is the ECU?

Put some fuel into the carburetor throat and see if it will hit while cranking.

Engine make model & serial numbers please
Only the fuel injected models have an ECU

Now for a general help, are the plugs getting wet ?

bertsmobile1 said:

Engine make model & serial numbers please
Only the fuel injected models have an ECU

Now for a general help, are the plugs getting wet ?.

Click to expand...

Sorry JD call the interlock module an Electronic Control Unit. The Z520A has a 25 hp Kohler engine with an one barrel Keihin carburetor.

Look for a single conductor black wire that runs near the fuel line into the engine that has a single plug/receptical on it. Unplug this and see if your mower starts. If it starts, it's the CPU. This wire defeats the mower safety functions the CPU regulates.
I have a x304 and a X324.

Ray52 said:

Look for a single conductor black wire that runs near the fuel line into the engine that has a single plug/receptical on it. Unplug this and see if your mower starts. If it starts, it's the CPU. This wire defeats the mower safety functions the CPU regulates.
I have a x304 and a X324.

Click to expand...

This trick works for your tractors. You are referencing the ignition coil kill wire. He has a zero turn, and he verified he has spark. To the OP, if your carburetor has a fuel shut off solenoid on it, do you hear it 'click' when you turn the keyswitch on? Those plungers can stick and not allow fuel to get through the carb jets.