Vapour Lock Caused by Winter Gas?

[Avenger Bob]

I have had the same problem on the first hot day of spring for the last three years and I am not sure what the cause is.
All winter my 2008 Avenger with a 25 hp Kohler runs just fine. When the warm weather comes it has stalled out, starving for gas, and refused to start until it has cooled down. It has done this the last three springs. When I pull a spark plug it is dry, even after cranking the engine for a very long time. Clearly fuel is not getting to the carburetor. When I pulled the Yamaha water separating fuel filter I had installed, it was only half full of gas.
I have wondered if the cause is vapour lock in the fuel pump caused by running with winter gas in the hot weather. (In the part of Canada where I live gas is blended differently in summer and winter. Summer gas is less volatile.) When I fill it up with new summer gas there is no problem, it runs just fine and always starts.
Or is it caused by my filter? Condensation in the gas tank in winter is a problem around here so I installed a Yamaha 10 micron water separating filter. Now I have no running problems with water in the gas but does the water clog the filter? Each time this has happened I have put on a new filter, but when I pour the contents of the old filter out into a glass jar there is so little water it does not settle out. The filter does not appear to be clogged. Leading me back to the conclusion that the cause is vapour lock and winter gas.
Has anyone else had this experience? Is it really the gas or something else?

[Avenger Bob]

My further research may have answered my own question.
I found the following discussion on another blog, The Mechanics Stack Exchange:

https://mechanics.stackexchange.com/questions/40459/fuel-pump-suction-performance

The key is the following paragraph taken from that post:

The way a normal fuel system is set up is; the fuel pump lives inside the tank. The pump lives in a cup that is fulled with fuel. The pump can draw fuel from either the cup or the tank through a sock. The sock is a light filter that keeps particulate matter out of the pump.

The pump then pushes the fuel though the filter. You never want to pull fuel through the filer. When this happens a vacuum would drawn on the fuel causing it to evaporate and vapor lock the system. Even without a filter mechanical pumps that are on the engine had problems vapor locking because they were pulling fule from the tank with a suction. This is the reason mechanical pumps have universally disappeared.

Of course the Kohler has a mechanical pump on the engine. I will move my fuel filter, reroute the lines and see what happens while I still have winter gas in the tank. Other years the problem went away after I switched to premium summer gas.