1994 90 hp issue

[kodiakmike]

With no load on motor, revs up fine, does not miss. Under load will get up to about 2000 rpm and it dies. This is every time, warm or cold. Took it to mercury dealer, they changed plugs, adjusted spark advance, replaced fuel pump diaphragm, changed fuel filter, used different fuel can (bypassing onboard tank) checked vacuum, compression is 130,130,128, and run through mercury troubleshooting guide and all electronics are within parameters, STUMPED!!
Any ideas?
FYI Motor is on a 18ft spectrum, prop is fine.

 

[kodiakmike]

Oh yeah forgot, carbs were cleaned and synced

 

[racerone]

Use a scope and check for cylinder sleeves loose / out of position.------Check flywheel key too.