Mine does exactly the same. Reasonable cranking speed to pull fuel up from the tank after standing for a week or so is needed too. If you have a pair of jump leads, try jumping from the negative battery terminal to the engine block. Does this cure the problem? If so, there is a poor earth connection somewhere. If not, remove it and try taking a connection from the postiive to either the starter (or in my case to the isolator switch which is mounted on the bulkhead above the toolbox). If that cures the problem you have a problem in the live feed connection. If not, then you are down to starter motor / solenoid...
Cheers,
