It sounds fuel related for sure. It idles fine but then won't take off correctly? It really sounds like a clogged jet or jets. Mainly your pilot circuit since that works until 1/4 open throttle or so. I would just replace 'em to be honest. You can clean them but you have to be very careful since they are brass. Blowing it out with air sometimes just doesn't do the job.

2008 Speedy, AI removed, DIY airbox destruction with K&N filters, spectres, re-jetted and "custom" rattle can paint job.