Alfa 33 4wd 1.5 Idles Roughly

[AMRI]

I HAVE A 1986 4WD 1.5 WITH WEBER CARBIES, IT IDLES ROUGHLY, BUT AT ABOUT 3000RPM, THE ROUGHNESS DISAPPEARS, THERE DOES NOT SEEM TO BE ANY SIGN OF A BLOWN HEAD GASKET, THERE IS A LOUD HARD SUCKING SOUND COMING FROM THE LHS FRONT CARBIE THROAT THAT FEEDS LHS FRONT.
ANY IDEAS OF WHAT COULD BE HAPPENING HERE, AND HOW TO STOP IT HAPPENING??