Not weird at all.  It's running too lean, or you have developed a vacuum leak, which would also make it too lean.

Check all the vacuum lines closely.  Pinch or plug them one at a time to make sure they are not leaking somwhere away from the carb.  Check the PCV valve.  Use some carb cleaner or propane and check for vacuum leaks at the carb base and intake gaskets.

If all of that is okay, run a good carb cleaner through the system (in the fuel tank) and use a spray down the carb opening.  It's likely that the jets and/or passages are starting to clog after sitting for the winter.  Did you use fuel stablizer?  If none of this works, you may need to open the top of the carb, pull the jets and mixture screws, and clean the passages.

But a really good cleaner may do the trick without a teardown.  The best I have ever used is Justice Brother Carb cleaner.  Some brands of carb cleaner just don't work.

I hate when the obvious is overlooked. I have done that many times. I bet it was starring you right in the face and never gave it a thought. Your hearing must be going too since a vacuum leak will cause either a whistle or hiss. It might be a good time to invest in some new vacuum hoses and connectors to replace the old brittle ones.