TOPIC:

2024-03-19 Top Airbox Install w/ ShimsSimply could not get the top airbox to fit by myself. And no help to be found. Get one side started, the other side pops off. Not to mention the center carb connection.

Solution? Wood shims! Worked GREAT. The pressure allowed me to manipulate the boots to fit over carb mouth.

 

I had had the same problem.  I wound up doing something similar sticking a piece of wood or crow bar or something in there to push it on evenly across.

The solution is as easy as loosening the carbs on the mounting bracket and applying some silicone lube to the "boots'. Once retightened the carbs will be aligned for subsequent reinstalls.  This applies to any time the carbs have been separated.
THEN do your "sync."
By design, the "boots" also have some inherent individual movement in the air-box. 
Having to shim, pry and force should have suggested "something" was misaligned !  

The upper airbox is somewhat deformed from years of heat cycles. And I need new boots too, as they tend to easily dislodge from the box. I'll eBay a used airbox assembly and buy some new boots. 

I did loosen the carbs and jiggled them around for the best fit.

Part of the problem is my arthritic hands. Just can't apply pressure like I used too. Sigh.

I agree more with Scotch's answer.

Previously, the carburetor flanges are loosened and the rear part is raised a little.

I greased the boots with oil and inserted the carburetor boot on the left side using pressure with the palm of my hand.

 

Without stopping to apply pressure with my left hand, I give a strong blow with the palm of my right hand and the boots enter by themselves.

 

Call me primitive if you want but using the technique of freeing a stuck drawer has worked for me every time.