Super M carburetor valve

2) Float dragging against carb. bowl. Take off carb. & Twist it in you hands in various positions. You should be able to hear or feel float moving on it's axle.

3) Float filled with fluid from leak. take off & shake float, even a very slight amount of fluid in float can keep it from working properly.

4) various other problems. I have actually had a beatiful looking carb inside & out leak gas & the only way I found the problem; I filled the carb. bowl with gas while I had it apart and found a tiny crack internally in the housing totally hidden from the naked eye.

5) usually the first thing I have a customer do though is to make sure needle valve is clean then try bending the float down a small amount. I have a gut feeling that the newer valves are somehow different than OEM causing these leaks either from imprecise manufacturing or poor materials. Nothing I can prove though. But most times bending the float down will cure the problem.
Good Luck!

When you replaced the needle did you also replace the brass seat? Could be there's a burr or something on the seat that's cutting the viton needle tip. Also are you by chance using a fuel additive or gasohol that's attacking and softening the tip?