225 opti wont turn max rpm

[loxboy1]

I recently replaced my 225 optimax with another 225 opti due to a blown power head. The prop came off the orig motor which has been on the boat for years and always performed great and turned up max rpms 5600.

Now with the replacement motor im getting 5200rpms max and thats with the motor trimed very high. If i run the motor at the trim level i used to it only gets 5000rpms. Ive checked coils, replaced plugs with ngk izfr5g gapped at .031 and new thermostats still wont get up to 5600rpms

 

[schematic]

start with the basics....
gear box ratio same as original?
compression?
spark?
fuel/air pressure checks?

 

[loxboy1]

Lower unit is off the original motor. Compression was taken cold on a somewhat week battery but showed 95psi balanced on all 6.

Bought a inline spark tester and verified spark on all 6. Dont know how to verify a coil isnt cutting out at higher rpms though.

Have not done an air fuel pressure test yet, waiting on the gauge. Motor is hard to start when cold or sits for more then a few hours.