If I were you, instead of gluing broken pieces together, I'd just buy the part to replace it. Look up on Ron Ayers Motorsports - Motorcycle, ATV, Jet Ski and Generators Parts and Accessories
or My Star Prompt - Parts Catalog
to find the specific part number. Then call your local Yamaha dealer or order it online. You already have it all apart...just replace the plastic piece. It sounds like it probably isn't a very expensive part and you won't have to worry about the glue coming undone, cracking, etc. and having fuel leak later.