Re: Having trouble with build
Looking at your photo I see you have the good old NT carburetor. That makes things easy as far as idle speed. There is only one external adjustment on the NT and that is the idle speed screw. Left side, the one with a spring under the head. Screw it in to increase idle speed and out to decrease.
How is your clutch adjustment? Is the clutch fully disengaged when you squeeze the handlebar lever? If not that will prevent the engine from idling. You want little to no slack in the cable where it attaches to the clutch actuator arm on the engine.
I'll also suggest you tighten the chain a little. 1/2" to 3/4" slack is where it needs to be. Yours is too loose.
Let us know if these suggestions help.
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