THanks for writing. Do you prune your plant? Because it blooms in spring, the best time to prune is in late spring, right after others in your area have finished blooming. If you prune in summer, autumn, winter, or spring before it would normally bloom, you could be cutting the flowers off before they have a chance to finish developing.
Also, when you say partial sun, does that mean it gets any afternoon sun? If not, the plant may not be getting enough light in order to bloom well. These vines do best in full sun.
Do you fertilize it? Too much fertilizer can encourage all leafy growth at the expense of blooms.
---Justin, Senior Garden Editor, BHG.com