Propeller vibration following carburetor synchronization

I have not touched the spinner since the calendar inspection last August, but I checked it anyway, no issues noted. I did however remove two washers from under the head of two nuts that secure the spinner to the backing plate, these were added last year during my one and only dynamic balance. I then went out and flew it today and interestingly the vibration was much less noticeable, the pedal buzz is gone but I still felt something, seems to now be a lower frequency vibration. Odd.  Gotta get in somwhere and get another dynamic balance.  

Try it without the washers. I had my C-182 balanced and just ended up with a different vibration, in the end it was a bad spark plug and I did not need any weights on the back plate. I also kept thing why would a new Cessna need a dynamic balance, it just did not make sense.

Following up, I performed a dynamic balance today and initial accelerometer reading at 5,000 engine RPM was .29 IPS so definitely unacceptable.  I ended up using about 2 grams additional weight as compared to what was installed on the spinner during the first balance about two years ago (performed by someone else). Also had to move the balance weights about 30 degrees as compared to where they were installed on that original balance. Ended up a bit smoother as well with .03 IPS as compared to .07 achieved on the previous balance. However, I still have no idea why I needed to rebalance after completing a carb synch but all’s well that ends well.