Yamaha outboard question

[jwclbi]

I have a 2004 70hp yamaha 2 stroke that is very very difficult if not impossible to start when cold, without the use of starting fluid. It is a carb engine with no manual or electric choke. It has what is called a prime start system. The carbs are clean and floats are in working order. I've done some research on this and although it isn't too common there are others who have had the problem but no solution. Any ideas would be great, thank you.