As to the fuel line.
You are not looking for crud but an air leak. Fuel pumps hate air leaks!! Especially at an Idle!!
Try a couple of wrenches at the intake side of the pump or screwdriver and while you are at it run you hand along the fuel line and see if you can detect any fuel.
When you replaced the fuel tank did you use the same cover with with the old pick up and sending unit?
Does the problem seem to happen at about the same fuel level?? You motor to the race and then and then to the fuel dock and it starts fine after that. You motor to race and it runs ruff and you don't go to the fuel dock and it wont start?
Because this problem only happens after long runs (hours) at 75% throttle I am ruling out--
Vent--if it supplied air for that long should be good for idle.
Fuel pump--if it can supply fuel for hard long run it should provide fuel for idle, you can try running it at full throttle and see if the engine surges--a sure sign either the pump is going or the filter is not passing enuff gas.
Idle jet--clean fuel filter should keep it clean and if it was plugged it would be pluged.
Coil--usually shuts off like a timer and then works after cooling.
Condenser--when it goes it goes.
I will check the other forum for assistance, thanks.
The fuel line doesn't really run past anything that is really hot. Not to mention that allowing the motor to cool, overnight, doesn't always solve the issue.
I doubt the problem is crud in the tank related. Over this past winter we replaced the fuel tank with a brand new one. The problem existed before and after the change. I will admit, although we replaced the tank and the filter, we didn't replace the fuel line itself. It looked in good shape, and no gunk came out when we blew it out with compressed air.
If it was a fuel additive or such causing the problem, wouldn't it have issues all the time? And without changing fuels, what would then make the issue go away?
I'm not trying to discount anyone's ideas. We have been working at this problem for a long time and are quite frustrated. Thanks for the help.