I've been having some carbonation issues and could use some help. The engine in my car is a modified 289. It's got 10.5:1 pistons, 351 heads, 0.10 cut from block deck and heads, MSD ignition, Edlebrock Performer intake manifold, and headers. I used to have a Holley 675 Street Avenger carb on it but the carb had been modified and ran very rich. I tried rejeting it but couldn't leak it out any. It was suggested to me that the carb was too big and I mistakenly (I think) switched to a 570 Street Avenger. The engine runs well under normal conditions but leans out when I get into it even fairly hard. I don't know enough about carbs (clearly) to solve this on my own so I'm hoping I can get your advice. I've been told by a guy that runs a local shop and races that the Street Avengers are good for stock engines and that I should use an HP carb for a modified engine. He suggested a 650. Someone else suggested that the mechanical secondary setup is not great for street use and a 750 vacuum secondary carb would be better. What do you think? How can I determine which would be best without wasting a bunch of $?