At cranking RPM a slightly low float might not create the pressure you need to get the gas to the engine. Cold motors need a richer mixture to start (thats what the choke is for). I would make sure your chokes are working first. At running RPM you would not notice a slightly low float because the pressure is great enough to get the fuel to the engine. You said you cleaned the carbs out, you may have bent the tab on the float a bit accidentally especially if you pulled on the float too much to clean the bowl instead of taking if off the pivot pin (hinge). There is a tab on that hinge that you bend SLIGHTLY to adjust your float level. I really think you need a manual. You will need to measure your float level from the bottom of the bowl and it needs to be where the manufacturer wants it. Adjusting your float level is not a way to compensate for a rich or lean air:gas mixture. Usually, but I cannot say ALWAYS, the float needs to be even with the bowl body WITHOUT the gasket on it. If your float pin is visibly worn you will want to replace the float.
If your engine is a 2-stroke I would not spray carb cleaner in it to start it. There is no oil in the carb cleaner to lubricate your pistons. If you need to, pre-mix some gas and oil to use as your starter fluid.
Like above though, I would also check the primer bulb, and make sure there is no air leak before the bulb. Also could check your fuel pump and replacing the fuel filter wouldn't hurt.
Edit: Some carbs have a window on them so you can see the fuel level in the bowl. If yours doesn't, you can run a clear tube off the the drain on the bottom of the bowl and hold it up next to the bowl to check the fuel level, but this won't help you unless you know where the fuel level should be.