Vacuum leak?

[rogus]

Installed a quick fuel slayer on my 355 sbc. It runs at high idle and kicks down to normal idle fine but as soon as I put it in gear it starts to idle rough and die. Any ideas? The engine is slightly modified but pretty close to stock. Its got a edel brock performer dual plane intake with a melling cam a little better than the old sbc 929 cam and 9 to 1 compression

 

[1320John$$$]

Check for a vacuum leak under the rear bowl Near the base plate you can spray a little break clean or carb cleaner and see if the idle changes