My moonflowers are also all foliage and no flowers here in NJ in August. My experience has been that I should not expect flowers from moonflowers (and morning glories) until the end of summer. They are late bloomers. Having said that, I see from your description that your vines are growing up your deck. How close is your lawn to your vines? If you have been fertilizing your lawn, you have also been preventing your vines from flowering. Fertilizers for lawns are high in nitrogen to keep them green. Nitrogen is good for foliage and bad for flowers. You will need to counteract the nitrogen with phosphorus. Use a fertilizer that is formulated specifically for flowering plants or one that has a high middle number which is the phosphorus.