strange idle

Check to make sure the advance weights aren't hanging up as mopower suggests also check the throttle shaft for excessive play (one sign of worn throttle shafts is a varied idle )
Also I have seen where big cams pull such a demend on incoming air requirements that they don't let the thropttle pull down closed after being reved up (you may need to drill the throttle plates to let it close again. )
Also check any vacuum hoses you have on this carb to make sure they arent holding open any choke pull offs or egr valves etc