My 150 merc does the same thing  sometimes she's good and sometimes she runs hot, what so you expect from a women  lol   With the merc you also have a poppet valve that would cause overheating   Don't know if yamahas have them
		 
		
		
		
		
		
		
			
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				love to fish 
			 
		
		
		
		
		
	
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