Only male flowers on my bitter gourd and bottle gourd with very few fruits setting

It is normal for cucurbits to produce many male flowers first and fewer female flowers, but a strong imbalance with poor fruit set is usually due to growing conditions rather than disease. Very high temperatures, too much nitrogen which pushes leafy growth, and poor pollination all reduce female flowers and set. Reduce excess nitrogen and use balanced nutrition with adequate phosphorus and potassium, which favour flowering. Encourage pollinators by avoiding insecticide sprays during flowering hours, and hand pollinate in the early morning by touching a male flower onto the female flowers, which reliably sets fruit on gourds. As the season warms and vines mature, the ratio of female flowers usually improves. Some growers use a recommended plant growth regulator to increase female flowers, but only on KVK advice and at the correct dose. Avoid spraying insecticides at flowering time, and ask your KVK for the local recommendation.