1993 90hp mercury 2 storke detonation

[roob76]

ok i have a 90hp mercury 2 stroke 1993 model year. the motor has a miss. every time it misses there is pressure going back into the crankcase and out of the carbs. i believe this is detonation and don't understand why the pressure seems to be comming out of the carbs. the reeds should close if there was pressure comming back no? if there is a broken reed could this cause detonation? also the carburaters are not responding correctly.

when the idle mixture srew is turned out counter clockwise it should bog down due to a rich mixture right? mine starts to idle faster as if more air is comming in. not sure what is gong on here or what to check next.
any suggestions will be greatly aprecciated.