Here's a simple check for you. Leave the bowl off, turn the fuel petcock on and gently, very gently, push up on the little brass fork that sits on top of the float. If the fuel stops flowing then the needle valve is working properly and clean. If it doesn't then look for trash stuck in it or a damaged or misaligned needle/seat. As was suggested you can carefully bend the fork fingers downward slightly, just a little, and see if lowering the float level doesn't cure your problem. The lower the float, the sooner it shuts off fuel flow into the bowl and lowers the fuel level in the bowl which can slightly lean your mixture. Make sure you bend both forks the same.
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