My 96 is giving a flooding problem.
I am pretty sure it is the left carb as the level goes up after about 30 second and petrol runs out onto the floor, but I cannot see from where.
I have monitored the level rising in pipes from the drain screws.  The right appears to be steady.  The left rises slowly when the engine runs until it runs out from....somewhere as I cannot see where. 
When stopping the engine the level slowly drops back to just above where it should be. 
Before I strip it down, I would like to know what I am looking to repair!
My sense of smell is very poor post covid, so despite this I am thinking that it is flooding the airbox/engine until below the flood level when it then remains approx 5mm above the correct level......hence the easy starting without using the choke.

Your thoughts please.

Nigel

Your test is U tube in carb drain?

You have two things involved: the float and the float needle valve, actuates by the same float.
Open both carb bowls and compare float height.
Clean or replace float valve on ill side.

With carbs as long it is working I prefer not to touch it. New spare parts a lot of times doesn't have the same fit or quality.
One adjustment at a time.Troubleshooting will be way easier.

JIS screws in bowls? Recommend changing to Allen. If you are struggling to take them out hammer then or use impact drive with love, put the metal on solid place to give support underneath the bolt, to avoid breaking a chunk of carb.

In extreme cases gas can get into the oil, inspect oil, try to smell it. put bike in center stand so it s nose is pointing up.
Anyways when you have all this done and sorted out after a few days with no troubles, change the oil just in case.

I really don't believe in the gas inside oil thing but is possible with a downward slope and an open intake valve, if not it should go to the air box.
Close petcock when not in use. You use it in On or prime?

Also you can test the bowls with air, sucking/blowing with your mouth, or maybe a syringe, with the carbs out you can flip them to see if they are sealing.
Maybe you have yini bit of debris and nothing more.

If you open them the point of the needle valve should be continuous like a new pencil, no slopes or notches. When it's starting to get tired it de forms where it seals. It's a rubber cone on a cylinder seal.

Armandorf,
Thank you for your reply.

I have stripped down the left carb, which had the higher fuel level in a pipe taken from the drain casting built into the bottom of the float bowl.  I pushed a nozzle cleaner through the hole, which was clear and using a flattened end of a small paint brush, cleaned the seat by rotating it.  I did nothing else on the bottom end of the carbs as as it ran quite well considering it was flooding previously. I did however check the slides, which were fine as were the diaphragms.
Upon trying to start the bike again albeit using a battery with little life, it will not start, but has backfired in the exhaust very loudly twice.
As I have changed so little, I am quite surprised it will not start.  Other than the petrol etc pipes which are quite complex considering it is only a twin(two petrol taps etc!).......any other ideas?  I have not checked for spark yet but given the backfire, I don't think it's ignition related.  Yes I can strip the carbs down, but might need a kit and I am avoiding that as not wanting to fix what is not broken given its easy starting and reasonable running previously.

did you check bowl level again? try to fill the bowl just enough and start it, petcock can fail an like its in pri, but the floats should limit amount of gas. look for air leaks

I eventually put the carbs in an ultrasonic cleaner with the main and idle jets removed. New 'o' rings and main jets as one was 122.5 and the other 125 gave good results. I also raised the needle one notch as it has a Nexxus exhaust fitted too  It was only a cheap Chinese kit, so no idea of the jet sizes.
Now at 17 degrees C it needs a little choke from cold for a few miles, so just about right. 
It pulls off idle well and handles a treat with a genuine Koni shock and 80mm shorter fork springs/sae 20 oil with 85mm spacers.  For me at 240lb it handles just fine, firm but not harsh and I am very pleased.
 

cONGRATULATIONS, YOU MADE IT

Many years ago I had a flooding issue with my carbs. I checked the float heights, they were fine. Needles looked good. I had also thoroughly cleaned out my carbs only a few months earlier with carb cleaner. Emptied a whole can in them. As it turns out, the seats were the culprit. The needles were sticking open because of some surface roughness or varnish (not sure what exactly). All I needed to do was dab some Brasso on the end of a cotton cue tip and polish the inside of the seat to a mirror finish by hand. Took no effort really, and the problem went away. Turns out carb cleaner can't fix surface roughness or deep varnish without some physical contact.