89 85hp bayliner ran good on muffs than died when put in water

Thank you for your help in advance.

I have an 89 bayliner with an 85hp force motor in it. I purchased a few months ago, I ran in in the drive way with water muffles on for about 2 months while doing the upholstery ran fine, accelerated well, went into reverse, had high a boat mechanic come by and he adjusted the idle he stated it was running high, now previously it had a little trouble starting if I didn’t hold the key in and turn to on position, but once it started it ran good (on the muffs), after the mechanic left that evening I turned it over and it started first try after having the idle turn down. Still starting on firs try few days later, So feeling confident I took it to the river, it started right up but sounded like it had loss all its power, then after trying to give it some throttle, it dies, fires right back up but still sounds like it does have enough power. After about 5 starts I pull it out the water. Now on muffs it will start and die out after 8 seconds and faster if I try to give it any throttle.

the mechanic also said i need a sifter (not having a way to put boa in neutral to warn it up without having the prop spin)

Try pumping the primer bulb while running in gear! what do the plugs look like when she stalls,wet, dry. Are you getting spark on all cylinders? Has an open air gap spark test been run?

Try running with the cowl off, possible the exhaust hose in the lower cover is leaking exhaust,
or the seal between the block and adaptor plate is leaking exhaust.

Okay I will try pumping the primer bulb once I put the carburetors back on, took them off to clean them. Good purple and royale blue spark, 90 psi in all three cylinders , carbs look Good so far, do see any visible blockage, spray carburetor cleaner through whole hole it comes out another.

I'll also try a open air gap tester not sure what that is yet but I'll look it up.

Okay how will I know if it's leaking exhaust , well there be water inside the outdrive ?

Would a. open gap tester be necessary if there is no gap

The "open air spark test" use the spark tester I posted.
That shows the strength.
It should jump 7/16" or more.

Leaking exhaust: the cowl will have smoke inside.
Maybe some water but probably not much.