The IP has a fuel suction pump.
Is there a fair amount of unburnt fuel smoke coming from the exhaust while you are cranking it over? If not I would say that the fuel is draining back to the tank from the top fuel filter. There are two check valves on the engine side of the primer pump.
There is an easy way to check for valve leakage.
Run the engine up to normal operating temp then clamp off the fuel line between the hand primer and the filters, then shut down the engine.
The following day (with the fuel line still clamped) try starting the engine.
If it fires up normally I would fix the check valves.
Here are some PNs, double check these with your local dealer.
SEAL fitting PN: A7982 /1 needed
SEAL valve PN: 73692 /1 needed
SPRING PN: 75866 /1 needed NOTE:This may not be needed if your spring is not damaged.
SEAL valve body PN: A17526 /1 needed
VALVE, LOCK PN: F10076 /2 needed
This is the whole primer unit if you want to go that route. List was about $136 + tax
PRIMER/A PN:75092 /1 needed
Hope this helps you.