75hp 3cyl 2 stroke backfires from exhaust no power

Hey, i have a 75hp mercury 3 cylinder 2 stroke. it barely runs and backfires out of the exhuast a lot.
serial number is 0D253026

it was at a shop and the replaced the stator with the red one and put the voltage adaptor in it.
it still runs like ****

things ive done; check fuel (good fuel no water, tried a different tank with another line and primer bulb)
went through and cleaned the carbs (thorughly cleaned them and installed new carb kits)
ive tried new coils from another engine that is running
tried another triggger
tried another rectifier
tried another flywheel (same style with permant magnets)
check keyway on crank to fly wheel (good)
new spark plugs
checked compression (105 psi all around)

what should i do next? backfiring out of the exhuast makes me lean towards ignition problems?
if it was reeds would it backfire out the carbs? thanks

Check all wires are going to correct terminals.----How did it run for you last year ?----Did this problem develop suddenly ?

Sounds like lean or timing to me. Cleaning the carbs means disassembly and soaking in Berryman Chem dip for a couple of hours then flush with water, blow dry then reassemble. Set the low speed jets from a light seat out 1 1/2 turns. Back further out 1/8 turn at a time till the backfire goes away. Also link and sync throttle pick up to .040" gap after you have adjusted the idle timing. Factory service manual is a must to getting everything set correctly.

So wires are all where they should be, I had this engine given to me they previous owner said it had week spark so he took it in a shop put a new stator in it and it was good for a while then it started acting up so he was done with it and didn’t want to fix it anymore. Is there a way to post videos?

I would be pulling the exhaust cover to inspect pistons / rings.----About 20 bolts and easy if it is a fresh water motor.----Perhaps you got a free motor with more issues than you might think.

It’s got good compression tho, looking at it the trigger doesn’t move and is kinda stiff the move by hand, it looks like the stator is touch the arm of the trigger?

Maybe this crap arctic weather has hardened the grease and won't let the trigger move, remove and grease with a light type like Mercury's 2-4-C.
Since it's firing thru the exhaust it means the timing is retarded, do you have a timing light to check it with the flywheel decal?
Can't understand the 2nd part of your question.