I have a kohler 3.5 marine gen. will ot start it is pumping fuel, bled lines. took air intake cover off. when it turns over there is blowback thru the air intake.

You still have air in the fuel lines. Get the air bled out of it and you'll have no problems with starting.

we dont have this engine here, USA.
but i have the WG jeep book,
starting page 12 , chapter 14


FUEL INJECTION PUMP BLEEDING
(1) If the fuel injection pump has been replaced,
air should be bled at the overflow valve before
attempting to start engine.
(a) Loosen the overflow valve (Fig. 18) at the
rear of the injection pump.
(b) Place a towel below the valve.
WARNING: WHEN CRANKING THE ENGINE TO
BLEED AIR FROM THE INJECTION PUMP, THE
ENGINE MAY START. PLACE THE TRANSMISSION
IN NEUTRAL OR PARK AND SET PARKING BRAKE
BEFORE ENGAGING THE STARTER MOTOR.
CAUTION: Do not engage the starter motor for
more than 30 seconds at a time. Allow 2 minutes
between cranking intervals.
(2) Crank the engine for 30 seconds at a time to
allow air trapped in the injection pump to vent out
the fuel injector drain tubes. Continue this procedure
until the engine starts. Observe the previous WARNING
and CAUTION.
(3) Tighten overflow valve.
HIGH-PRESSURE FUEL LINE BLEEDING
WARNING: THE INJECTION PUMP SUPPLIES HIGH-
-PRESSURE FUEL OF APPROXIMATELY 45,000 KPA
(6,526 PSI) TO EACH INDIVIDUAL INJECTOR
THROUGH THE HIGH-PRESSURE LINES. FUEL
UNDER THIS AMOUNT OF PRESSURE CAN PENETRATE
THE SKIN AND CAUSE PERSONAL INJURY.
WEAR SAFETY GOGGLES AND ADEQUATE PROTECTIVE
CLOTHING AND AVOID CONTACT WITH
FUEL SPRAY WHEN BLEEDING HIGH-PRESSURE
FUEL LINES.
WARNING: DO NOT BLEED AIR FROM THE FUEL
SYSTEM OF A HOT ENGINE. DO NOT ALLOW FUEL
TO SPRAY ONTO THE EXHAUST MANIFOLD WHEN
BLEEDING AIR FROM THE FUEL SYSTEM.
Bleed air from one injector at time.
(1) Loosen the high-pressure fuel line fitting at
the injector (Fig. 19).
(2) Crank the engine until all air has been bled
from the line. Do not operate the starter motor
for longer than 30 seconds. Wait 2 minutes
between cranking intervals.
(3) Start the engine and bleed one injector at a
time until the engine runs smoothly.

end quote.
pump timing is on next page
or tank filter line priming before. above.

check for power at the fuel solenoid

not familiar with "Hipo" motor, but the early mercs had a filter under the fuel line connecter to each carb, then they started putting them under the intake of the fuel pump under a plastic cover.

Valve seats, valve integrity, intake seals. Perform a leakdown test to further diagnose

Once the fuel tank was empty the fuel line has got air locked and so the fuel pump will neot work unless the air is bled out of the system.
So open the cap to the fuel tank and using the palm of your hand to cover the mouth of the fuel tank try to blown to pressurize the tank.
if this wont work the fuel line to the pump must be opened and the fuel bled out.
Now the fuel will flow to the pump and start the engine.
Never run the tank dry.

The pickup tube in the craft's fuel tank has likely worked loose and dropped into the tank. The generator lost its "straw" that it needs to siphon fuel through.

if you have spark and fuel it should atleast fire when you spray fuel in the carbs. if your spraying it just into the air intake it may not be making it to the intake manifold. have you checked the fuel pump? you also need to check for the possibility of a air leak in the fuel system causing the motor to fail to run because it has a very lean fuel mixture. check all fuel lines, fuel tank, couplers and carb gaskets. if you havent take the air intake cover off and try spraying some wd 40 or other mildly flammable product and see if the motor will fire that way. its likely the fuel tank or fuel lines are the problem from my point of view. good luck.

If the engine is running rough then this could mean that you have weak spark or valve adjustment. When an engine runs rough it will not burn all the fuel, which will create excess fuel in the air cleaner housing. Also, make sure the the float is closing in the carberator.