S650, needs fuel filter purge to get going after shutdown

[Bostwick70]

Hi I'm new to this forum and too Bobcats, I've been chosen as the in house repair guy for our tractors, backhoes and such. I'm having a problem that I can't seem to figure out. Bobcat s650, I changed the fuel filter last month (so I don't think it's related) ran fine till a couple of days ago, it just stopped it had a 1/4 tank of fuel, I thought maybe it had suffered a fuel pickup line separation in the fuel tank, but no, I took it out and it has a fuel tube, no leaks, cracks, etc. I filled up the tank, purged the fuel filter, and now it will start, only after some starting fluid is introduced (contrast to when I changed the fuel filter last month, purged it and it would start right up). I replaced the fuel bulb since the check valve is in there from what I've read. After shutting down the engine for 15 seconds or longer, it won't start, it'll turn over, but that's all, it requires a fuel purge, significant amounts of air have to be purged and starting fluid to get it going, otherwise runs fine, but obviously wanting to get this fixed. I've have added a check valve just after the new fuel bulb, thinking if fuel was kept in check at that point it would prevent air, or fuel draining back after shutdown, but no, same result with two different, brand new fuel check valves. Any idea where I should look at next?