 
 Good point on shutting off fuel supply.
 
  If I don't start my engines every couple of days I have to crank for ever to get fuel up to carbs.
 
 I shut the valves off last night and will wait a week to see if this corrects the problem. 07/01/2020--
07/07/2020
Yes, I do have anti siphon valves at each tank and yes they are clean.

 
  
  