The tank must be filled with fuel, the engine must be mechanically in order, the battery must be charged, the starter must rotate at a sufficient number of revolutions, the ignition system must be in order, there must be no fuel leaks in the fuel system, the fuel system must be clean, the crankcase ventilation must be in order, and the electrical ground connection (engine - gearbox - body) must be present.
Caution: If removing fuel hoses, clean them with gasoline first.
