could be 1 of 2 things...
stuck float or failed petcock diaphragm.

pull the vac line off the carb and plug the vac port.
there should be no gas in the vac line.

float will sometimes stick open.
give the carb a tap with a plastic screwdriver handle.

I will change the overflow tube, the rest is done. Have checked carburetor and petcock at mc garage, everything ok

Something is NOT OK if there is gas flowing from the air cleaner.  There are only 2 ways to get gas flowing around the air cleaner.

1. It comes out of the carburetor.
2. Leaking gas tank above the air box and fuel flows down.

Are you sure there are no holes or a small crack that leaks with the vibration of the bike running?

That tube that is going down instead of up is actually a vent tube to allow pressure equalization between the bowl and outside.  If fuel is coming out that, the bowl is way, way too full and it's also bubbling up through the main and pilot jets. That is way above the top of the bowl. Float valve is not shutting off fuel flow.

So, If the float valve is not shutting off the fuel flow, and fuel is actually splashing out, it's got to be worse than just the needle and seat leaking. The float must either be stuck on the bottom of the bowl ( like Versy said, whack the bowl with something to shake it loose) the needle has somehow dropped out of it's place on the float or the float level is set way too high. All easy fixes. An outside chance ( and one I've come across only once) is the vent tubes. The two hoses, or at least one, need to be unblocked and free to flow air. If they can't, the fuel flows through the fuel tap into the bowl. The float wants to move up and shut off the fuel flow but because the bowl isn't vented, the air in the bowl can't get out. The float can't compress the air so it stays down, the float bowl fills with fuel and fuel pours out the overflow or carb mouth.

I found this once when a buddy brought a GSX250 with twin carbs to me. He'd cleaned the carbs and refitted but they poured out fuel. once the carb bowl was loosened, the flow stopped. Turned out he'd joined the two carb vents together with a hose instead of having them open to atmosphere. pulled that hose off and all was well.