There are 5 bleed inserts.----Found when removing transfer port covers.----Not found on the bottom cylinder.----Tiny nylon inserts.----Often have gone missing.-----It should not be hard to set low speed mixture screws.
Checked for missing bleed inserts ??---Low speed MIXTURE screws are to be adjusted with boat in the water and idling in gear.----Adjust ( rich ) till bogging goes away.
If it runs " great " , then why do you feel you need to adjust stuff.----Best to replace water pump impeller.----Test overheat horn.----Post compression test numbers and record them for future reference.
According to the parts book the primer valve appeared in 1983 on the 70 HP.----Something is unique to your motor.---Wrong ID plate or powerhead was replaced.
Does spark jump a gap of 3/8" ( 1 cm ) on all leads ?----The type of sparkplug has nothing to do with that test.----Might be running on 3 of 4 cylinders.----Clean carburetors.-----Remove lower unit and check for carbon blocking the exhaust.
