My V was doing the same, I made the hose the same, vents the same and still nothing! 
I did the same mentioned with a shut off on each tank, when one was getting empty I was able to catch it and turn the switch and was always good! 
When I converted from I/O I added another 25 gal tank in the motor well, and being I never used more then 25 gal gas just left that filled all the time and the saddle bags empty, boat always level after that
		 
		
		
		
		
		
		
			
				__________________ 
				1986 V20   
Old Fishermen never die, we just SMELL that way!!
			  
		
		
		
		
		
	
	 |