I had the same problem on my 84 Venture with 25,000 miles on it. I had my buddy that I ride with to test drive my 84 and he said that it felt like it was running on 3 cylinders. So I started taking out the diaphragms on the right side to start. The #3 was perfect almost looked brand new, so I put it back together and went to the next one, as soon as I got the cover off
the diaphragm fell out in pieces with the plastic still inside the carb. The #4 looks almost new too. My friend gave me some repaired ones to try,so
I put one into #4 and test drove later, Man this thing had great power from idle through the Red-line. Thanks Richard....Next has anyone put a diaphragm back together with Epoxy and had any luck, Richard said he thought the diaphragms maybe came separate from the plastic at one time. I appreciate any help Timthetoolman62