2003 Merc 15 hp 4 stroke choke problems

[Bighornbob]

I've got a 2003 Merc 15 hp 4 stroke, that will only run with the choke pulled all the way out. Any effort to inch it back--warmed up or not--kills the engine. I bought it new and it's done this since new, only it's worse now than ever. I've had it in to the shop 4 times to be fixed, 3 times when it was under warranty. Each time they said "it runs great now" and each time it's seen little improvement. Finally the dealer went out of business, so I've never been able to get it fixed. I've switched tanks with one that is known to be good and it is still bad. Fuel is fresh. Tank is clean. Someone said it might be a vacuum leak. Plugs have been changed. Fuel filter changed. Still same old problems. Ideas?