Apt set too lean could cause a stumble or bog. Weaker power spring could cause that stuttering thing too.
Reach in the air vent in the top centre of the carb with a small screwdriver and see if you can push the primary metering rods down while the motor is shut off. They should move down easily and spring back up. I've had them hangup on the gasket before.
How did you disable the secondaries?
What's the elevation where you live?
Apt could be set too lean!