Demon Carb Mods
The Mighty 650 doesn't have replaceable venturis or boosters, sorry bud. You could always give it me though and buy a Mighty 750. LOL!
All kidding aside, your combo could make use of more carb. BG has the new annular booster 750 and 800 cfm carbs out now. Here's the link:
http://www.barrygrant.com/news/articles/products/product_002.aspx
They should combine the throttle response you already have with the top end you feel you're missing.