Why won't the suzuki baja 300 atv start when cold?

I have a suzuki baa 300 atv and when it's cold you have to give it a shot of starter fluid in the air cleaner box to start ,but once is warm it start without doing that, I took the carb off and cleaned the main jet and the idle jet,cleaned the bowl and check the float for proper operation. I don't understand why it doesn't start when it's cold any ideas?