Re: 1995 150 EXEOM Idles to fast.
If it operates thru the range properly beyond idle I would look for an air or fuel leak, pressurize the system with the bulb and use a flashlight to look for wet hoses at all connections from the bulb to the carbs.
Gaskets around carbs and manifold gaskets. Slight air leaks will cause a lean idle which speeds it up. Make sure primer solenoid isn't leaking, air will be drawn in if fuel leaks out.
A timing light on the timing wheel will show if its double firing, match the spark plug wire number to the number that flashes on the wheel, don't point it at the optical sensor. I doubt thats the problem but I like to eliminate it.
You will need a timing light to ensure the timing is set properly at idle.
6deg ATDC.
If the idle timing is within a degree I would look for air leaks.
If its a carb seal problem you can try putting 2 fingers in each throat to see if idle calms down, thats the problem carb if it does.
Suggest you spend the $50 on a factory service book too, it will help you immensely. I think these guys have it. Best money you will spend on it.
www.outboardbooks.com