Yamaha outboard question
 

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.

Have you checked your primer bulb? Sounds like it may not be working correctly.

The one that was on there worked but I swapped it out anyway with a new one then one off my seacraft, same problem.

A "Prime start" system has a solenoid that either allows fuel to gravity flow into the carburetor throats, or a small priming pump that pumps a predetermined amount of fuel into the carburetor throats.

You need to determine if your priming system is working. Find the electric primer and follow the fuel lines from it to where they attach to the carburetor. Pull the fuel line from the top carb and put it into a small glass jar, like a baby food jar. Turn the ignition on and push the key into the ignition switch, activating the priming system. A small amount of fuel should flow into the glass container.

Early Mercury electric priming systems only pushed/pumped fuel into the top carburetor, while later versions such as on the XRi motors primed all the carbs.