can you help me solve this riddle?

[fair weather]

I'm desperate for knowledge from mechanical experts. My outboard is a 2005 60 HP Mercury, 4 stroke, fuel injected.

Here is the riddle.

If I go fishing on a cool cloudy day the motor operates fine. But on a sunny, summer day, if I run it far enough to heat up the motor, stop and fish for say an hour, more or less, then start the motor to move, this is the sequence of events. The motor starts then sputters (misses) and dies. And it will keep missing, like it is starving for gas, and die every time, no matter how many times you start it. Now get this! If I take the motor cover (lid or bonnet) off and wait 20 min. it will start and run fine.

If I leave the motor cover off it will start and run fine, no matter what pattern or running and fishing I put it through. If I put the cover back on the motor, it will fall back in the pattern of not running for 20. min. after I get it hot and fish for a while.

If I trailer it while it is having its "fit" it will start and run the next trip.

If I run it hard then stop and immediately start it , it will start and run. It seems you have to wait a length of time.

If you idle along as in trolling (and I've put 1,000 hours in trolling as per the computer) it will always start and run.

If it is acting up and I bleed the gas line where it enters the motor from the fuel tank, it will keep on acting up. If I bleed the gas line way, way up on the motor (a red quick disconnect) it will quit acting up and run right.

If I unhook the fuel injectors while it is missing then it keeps on missing like nothing was done.

My mechanic has tried new fuel pumps etc., etc., to no avail.

I wonder if this could be happening. The heat from running the motor hard plus heat caused from the sun shining on the black motor causes a "vapor lock" somewhere in the gas line. This new gasoline is high ethanol. Could it evaporate and lock up the gas line?
And if so what can I do to stop it? Or am I way out in left field?

What do you think?

I apologize for the long post but couldn't think of anything to leave out.

thanks
fair weather

[Bombfixer]

I think that your idea of some sort of Vapor Lock is spot on for a starting point. You could have rag in an ice cooler next time you go out. If (when) the motor starts to act up put the cold rag around the gas line and see what does. If it stops it then you could purse the Vapor Lock idea. If it doesn't then you need to look at other areas. Something else you could do is to check the "telltale" and see how hot the water is. Possibly you might have a themostat problem where the moter is getting too hot and the heat from the motor is causing your "vapor lock".

[strmwalker]

what i would do is go to the store and get me some marine sta-bil and a bottle of seafoam put in the tank and run it you might be surprised on what it will do for you!!!if you are getting gas with ethanol and not putting seafoam and or sta-bil in your gas you are play russian roulette with your motor!!!

[brushnjigs]

With the motor an 05 I hope you have changed the fuel lines and filter, if not , do it immediately . Check that the fuel line is not touching the block. Your doc may have to take the lap top and take it to the lake to check it under load. Run sea foam at all times with this crappy fuel we are getting these days. 1oz per gallon.