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If fuel is coming out from the air vent then the carb is over-filling. Fuel flows by gravity from the fuel tank/petcock into the carb by way of the float valve. The float valve floats up and shuts off the fuel when the right level has been achieved in the float bowl, just like the ballcock in a toilet cistern. The overflow you are seeing t means the float needle is not sealing, which could be a worn needle or seat or a bit of debris stuck in the valve. Sometimes tapping the carbs gently will dislodge a bit of crud and help it seal, but its probably best to remove the carbs and the float bowl for a good inspection/clean out. With the bowl off, you can just slide the float pivot pin out and lift the float and float needle out for a look/clean. The diagram is from the common service manual so you know what I'm on about.
I fixed the leak i was just dumb and switched 2 line in the petcock before this it did not run now it runs for 3 ish mins then dies. So know what do you think cause im just lost now
The petcock needs vacuum to open it to let fuel flow, so if there's no vacuum you will run the carbs out of fuel. The fitting on the very back of the fuel tap needs to be connected to the vacuum hose that comes from the left side the carbs and connects to one of the intakes. The other fitting is just an overflow vent so the hose (if there is one) should disappear under the engine somewhere.
