Robin NB26 Brush Cutter\String trimmer

[BigPapaMax]

I have an old Robin NB26 string trimmer. A few weeks ago I replaced the fuel line, filter, spark plug and the primer bulb. Also cleaned the fuel tank out. Pulled the rope 3-4 times it fired right up and ran it for like 15 sec shut it off restarted it one pull ran for another 15 sec. Turned it off set it in the shop because I needed to get a air filter for it before I used it to trim brush\grass. Got the air filer installed it and it wont start now. So i ordered a rebuild kit for the carb. The diaphragm was pretty stiff. I thought this would be the issue. Put it all back together with new parts and a good cleaning. But it still will not fire up. I pulled the plug out it seems to have good compression and I grounded the plug to the head and pulled the rope and there is spark. It also seems to be fuel as well because the plug looked like there was some fuel on it. I did use the premix fuel that I bought at Lowes. Im going to try regular fuel and oil mix to see if that helps. Any other suggestions? Thanks for any help.

Charles