Ok the same happened to me, I had a big struggle with this floats and needle. Turn ed out the neeedle on the left carb could not move properly, It would move when I look at it and when I did visual inspection it would look excetly the same as the right one but no, sometime would move, sometimes wouldnt.
I had to movee the needle a little bit and try and try again and now it seems to work.
So my advice get some water, take the bulbs off and deep the floats on water, the needle needs to travel freely!
Within my service float needle replacement is automatic. They are consumables and never intended for indefinite service. In time the viton tips deform and the tiny, internal float return springs at the top fatigue. Cheap enough to justify replacement.
Then comes wet testing to determine fuel levels, the 17mm float height is a starting point to get you close....but begs final tweak wet on the bench or stand or whatever your method.
During a refurb, wet testing also reveals any leakage anywhere....double duty.
These EX's are getting old...all seals within them (also consumables) need replacement as well. Now we get into full "rebuild" "refurb" "restoration" territory. 15-20 year old carbs are gonna have problems attached, to some degree. Unreasonable to expect them to last forever.
IMHO best to be proactive, "rebuild" using new consumables, setup properly and thus turn back the clock to zero. It can be done....and is on a routine basis. Planned maintenance done at your chosen time.
OR....wait for a leak, running issue, poor MPG, fuel stink....then forced to become "reactive". Of course, it'll happen at the worst time imaginable.
Rebuild = proactive
wait for an issue = reactive
Entirely your call.