ive had a carby that had to have choke on half to ride, O ringed it, silicon sealant, no change. adjusted needle settings, no change. i fiddled till i couldnt fiddle no more so hit the company up, who sold motor, to give me a new carby at cost price. friends of mine have had same issues and resolved problem by lightly sanding needle. makes sense as i understand if not enough fuel is getting through less air is needed, ie choke on. try putting needle in a drill where the drill bit would go, even sanding. not too much mind you. baby steps.