2001 mercury 90 hp two stroke doesn’t seem to advance timing

[Flukinfool]

Greeting members,I am new to the forum and hope someone is familiar with the throttle assembly/timing advance on a 2001 mercury two stroke 90 hp elpt.Recently rebuilt the carbs with quicksilver kits,compression is around 115 on all three cylinders.Engine starts right up and idles fine,when giving gas it backfires through the exhaust.Did this before I did the tune up,new wires and plugs,spark is good.The butterflies are closed on the carbs before the roller hits throttle,just doesn’t seem to advance the timing when adding rpms.Thanks in advance.
BTW,motor is for my dads 1969 thunderbird that has been restored from the keel up.Anyone want to see pictures,Lmk.

 

[racerone]

Serial # of the motor ?----Checked the flywheel key ?

 

[Texasmark]

Can you set the idle speed in F gear with the boat in motion in the water at 675 +/- 50 RPM with the knurled white plastic knobbed screw on the spark advance lever?