120 force outboard runs on land but won't start in water

Ok I'm gunna try to get it all out my 120 force out board sat for six years I go the boat for free. I fixed everything and it now has a full tune up. The boat will start with the muffs on and run water or of the pee hole I guess it's call and will run it out of the propeller which the mechanic said was ok. Here's the issue it starts right up now in the drive way but in the morning after sitting all night it won't start in the water. My buddy and I got it started on land and backed it up into the water and it ran fine. We turned it off and started it up immediately in the water again and it worked. My idle on land in about 1100 and in water about 750. I get real sad about sitting at the doc everytime I try to take her out. I do all the work myself but I'm used to cars. Help me please. I need ideas I research night and day and can't figure it out.

Runing the motor at the ramp ( no water to the pump ) is a mistake !!------------Start with a compression test , then check for strong spark on all 4 leads.-------If those are good then carburetors may need to be properly cleaned.

All that is good strong spark strong compression . The carbs have been professionally cleans rebuilt and tuned. The out board had water in it still as it was coming outa the engine which is the only way I woulda started it outa the water.

Then it should run with no problems.

It does just not when u try to start it after it sits in the water I heard someone had an issue like mine and the problem they had was the idle exhaust thing

Take the engine cover off and check the rubber exhaust boot (on the inside of the leg housing) that is connected to the little "exhaust " holes on the back of the engine. If it has any cracks or holes, the exaust goes into the engine cover and kills the motor (no oxygen to carbs).