Agree with Hawkenbob, check the outlet hole, it should be flowing really well, not just leaking.... On my Honda with a jet, the hole just wasn't big enough to let the small debris out that the jet will suck up, i.e small plastic trash, tiny rocks, fish guts and other stuff.... It was as simple as drilling out the hole to a bigger diameter bit, re-tapping it and replacing the fitting and hose with a larger sized outlet. Almost every outboard was designed for prop and jet added to it later, so the sucking power of the Jet wasn't originally designed into the the cooling system of a prop...
If that doesn't work drop off the jet assembly and replace the water pump or at least tear it apart and clean all the sand and other crap that gets lodged in there. Good time to learn anyhow cause the last thing you want is the pump to jam on a river and you can't do anything but float it out...