proform race carb / Idle trouble

Hi Guys,

i´ve got a 750 cfm proform race carb for my 408sb. I could it get to idle halfway correct only with the idle mixture screws totally out, so far that theres no more effect when turning more. This makes me think if the idle air bleeds should be bigger for my application - or to decrease the size of the idle feed - is this correct?

timing is set at 18° at the moment, i adjusted this with my brothers edelbrock carb - with this one it was idling very good and had good response.

Thanks for info!

Michael