KZ650 Engine start troubleshooting

Hello, I spend the winter reviving an 80 KZ650 that was not started for a couple of years. With the help of experts of this forum, I rebuild the carbs, changes a bunch of parts and got the motorcycle running and driving smoothly. 
the only thing is that I could never start it cold without spraying starter fluide onto the air filter. 
I cleaned the bike 3 weeks ago after riding it for 45 min with no problems. 
Except that now that the weather is nice, the bike won’t start anymore!
it cranks and clean fuel is passing through the petcock but it seems it’s not igniting. 

is there a good troubleshooting method that I should follow?

When you rebuilt the carbs, did you verify the choke passages were open?

Yes I completely took the carbs out this winter, replaced all the rubber and brass parts. Cleaned it all in ultrasonic cleaner. 
the bike was running fine for several months. Until now. 
 I also tried the kick start and found that it was surprisingly easy to rotate. Shouldn’t the kick be hard?