I have kipor 6700 diesel generator when I'm trying to turn it on the starting motor works but engine doesn't start even though I tried for 8 times the battery is ok and oil level is ok 2- there is oil in the floor of the generator is this normal !? Thank you

missing ground maybe. switch should ground out spark

Check the glow plug system. Deisels are hard to start without the glow plugs not working, even if it's hot out. It's a mystery to me as to why it will start easily in the cool evening though, and not when it's hot. Be sure the injector pump timing and engine speed solenoid are working upon the switch be turned on. This solenoid advances the fuel timing, making it smoke a bit out the exhaust, and raises the engine speed at the throttle on the engine. If that doesn't work, neither will the engine, as far as starting that is.

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The function of diesel fuel system is to deliver the diesel fuel to the engine clean of of purities at the right pressure. In most generating unit diesel engines, the fuel system loop consists of the following major parts:
1. Day Fuel Tank
2. Fuel Water Separator
3. Fuel Strainer
4. Fuel Supply Pump
5. Fuel Filter
6. Fuel Injection Pump
7. Injectors
8. Return line to the day tank
Hope it can help you.
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is it air bound , clear it out , or you have a short but I would go with the latter ,

Yes, it IS normal for a powerstroke diesel to require more revolutions of the motor to fire than for any gasoline engine. Combustion in gasoline engines is stimulated by spark plugs and many gasoline engines will start with little turning of the motor past the position where the ignition timing creates the spark and combustion occurs. Combustion forces the engine to continue rotating and combustion in that and other cylinders becomes a perpetual event. A Powerstroke Diesel engine requires more revolutions and speed of revolutions to create the heat necessary to cause the diesel/air mixture to combust. ALSO, the diesel is injected into the combustion chamber, at high pressure, by the injectors. The injectors are electronically controlled and the Fuel Control Module (computer) (also known as the Injector Control Module or ICM) tells each injector exactly when to open and inject diesel into the combustion chamber, as well as for how many milliseconds it stays open (how much fuel will be delivered). Summary, a powerstroke diesel will only begin the perpetual combustion process when the motor is turning fast enough and the pistons are compressing the volume of the cylinder into the tight space of the combustion chamber rapidly enough to create enough heat for the fuel to ignite and begin creating power to turn the motor without the aid of the starter. IN ADDITION, a Powerstroke will NOT start at all with weak batteries. Not only does the motor need to revolve rapidly in order to start, the injectors require a MINIMUM voltage of MORE THAN 12 volts in order to activate (open). The exact amount of voltage required can be different, depending on the Fuel Control Module (FCM) or "Injector Control Module" (ICM) type that is installed. (Note; terminology for the FCM / ICM tend to depend on who you are talking to, what resource you are reading, etc. They are the same thing.) If batteries are weak, the starter uses enough amps to drag the voltage down and, even though the starter turns the motor fast enough that any gasoline motor would fire right up, the ICM will never send the signal to the injectors for them to activate so, the cylinders never get any fuel and the motor never fires. I hope that helps. Yes, a 7.3L diesel will normally need to turn with the starter for longer than your gasoline fueled V10.

Check your preheating plugs.

Some times the extra amperage coming from the alternator the diesel motor will burn out the electrical components of a smaller vehicle. This is why you should never jump start your lawnmowers, motorcycles, or any small engine with a full size vehicle. Check your battery, then alternator, and keep tracing it back until you find the source of the problem.

I would try changing your fuel filter. Inspect the fuel lines for leaks. Air getting in the line would cause fuel to flow back into the tank.
I really suspect that the long cranking time may be a problem not with the fuel system but with the glow plugs, You probably need to replace the plugs as they are not pre-heating the combustion chamber properly to allow ignition of the diesel fuel. To start a diesel motor with out glow plugs you have to crank the motor until enough heat is generated to ignite the fuel. Glow plugs are not very expensive and fairly easy to change your self.

That symptom is either the glow plug temperature sensor on the engine or a you have a burnt out glow plug or two.