If it runs better with the choke (it gets more gas)this tells you that it doesnt get enough fuel without choke.
If the jets hasn't been touched recently, I would clean out the carburator and maybe the tank and petcock (valve)
It can also be an airleak somewhere, but then there are many possibilities
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Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom