Carb overflow leaking

you probably could if they were/are on allen bolts, but your pretty limited as to what you can then do with them. its usually easier to take them off completely, that way you can clean things like the float valves and check float heights etc

Yes as the picture shows, but, to increase the driver bit pressure on the screws, a seesaw arrangement under the "rachet" ( maybe t bar better for this ) head

Push down your end, carb end pushed up, if you see what I mean.

It's a good idea to fit new Allan bolts to float bowl and upper chamber.

Then most if not all jets etc can be flushed and or blasted clean.

Don't remove the slow running jet needle from under the front of the carbs if they are still on the engine.
You can undo they all the way keeping them up in place, then screw back in two turns.

If you don't know why, see the carb exploded views in the parts books.

Be carefully about any diaphragms in the economy diaphragm chamber, the two screw chamber on the sides of the carbs, they are probably not fitted to 250 carbs but are to 400 carbs I think.

The right carb diaphragm screws will be near impossible to get at with the carbs fitted

Fuel level can be compared carb to carb via the float bowl drain screw system, as you will realise when inspecting them.

I have already been to the carbs on mine 2 weeks ago, after having the new, I say new, new to me, bike.

I flushed the tank and tap with loads of old petrol and rust coming out.
I have fitted a Volkswagen type inline fuel filter for now but I am finding out about a fuel tap with a sludge trap and wire screen filter. If I can find a small magnet to fit in the sludge bowl, happy days.

Fine rust particles in the combustion cylinder is not good.

Your carbs may only need a good clean be t is the overflow tube in the float chamber split at all ?

Stay safe out there

All piggin fiddly. I am reminded of that old joke about the gynecologist who decorated his hall stairs and landing whilst outside using only the letterbox for access !