Don't know what you are doing (which way are they facing, temps etc), but try moving them. Mine grow against a west facing wall and perform well.

Lord, hope someone comes up with a good answer for this one - I've never once managed to get Morning Glory to flower for me, in or out of sun, just get lots of leaves. I'll be keeping an eye on this question... but it occurs to me to wonder about nitrogen levels - if the nitrogen levels in the soil are high, it may be that this plant doesn't bother to flower... I haven't tried for years, I might do a bit of research. Are you feeding them Cynthia, and what with if you are?