I have a 1986 Hyster 60 that runs well but has some trouble starting. We have found that it starts if you lift the top of the Impco model 100 mixer and let a little bit of air in below the diaphragm. We replaced the diaphragm on the mixer and cleaned it out. It still has the same problem with a new diaphragm but it still has the same problem. I have done a lot of trouble shooting on the issue, but I think I am missing something on the troubleshooting. Does anyone know what might be causing this issue?