terraplane-
I think MikeMac is on the simplest, most longical track to explain your observation.
One carburetor float is probably sticking or not closing fully and when the motor is tilted up it's passing a small amount of fuel out the carburetor vent.
The cold temperatures could also be adding to this affect by shrinking the metal parts of the valve seat, enlarging the clearances.
Also, the recently added carburetor cleaner may have removed some varnish on the needle valve that helped hide some valve wear at the seat by making a better seal than the metal alone.
Your Honda 90 has four carburetors on it, right?
It's so small and since it quits after a few minutes, probably not worth worrying about, just keep an eye on it.
However, when checking the leak, don't be doing the Groucho Marx routine with the lighted cigar, or you may find the "magic word" to be "Fire!". :xlol
Joe. :thup :teeth