I have two chocolate vines
I've had them for about 4 years. They grow on a trellis. My question is that only one of the plants will bear a few blossoms in the early spring but it never produces any fruit. They receive several hours of morning sun, then light shade starting about 1:30 or so. They have well drained soil. They grow on the"sunny" side of some redwoods. I water them once a week. The vines are leafy and grow well, but I want to know what I can do to make them flower better and produce fruit.
The general diagnosis for non-flowering is that there is not enough sun, or too much nitrogen in the soil. So the first thing you could do is move your plants to a sunnier spot. This may sound like a lot of work, but remember gardeners often have to move plants around until they find the perfect spots for all of them -- and then they go and move them some more, just because. Another thing to do would be to add phosphorous in the form of bone meal. (I personally try to avoid using high-phosphorous fertilizer if I can because of the dangers to the environment of fertilizer run off.) You might also increase the organic content of the soil with mulch. Here's an article that might give you some more tips: https://www.gardeningknowhow.com/ornamental/vines/chocolate-vine/chocolate-vine-plants.htm