Another idle problem

[cymric]

I have a Johnson 15hp year 2000.
It has had a complete rebuild.
It will idle in a tank for ever, in gear and out.
If I take it on the water run at WOT for 5 mins, when i throttle down it stalls.
I can start it and it will run above idle quite happily.
I have new fuel hoses and I've rebuilt the fuel pump, the diaphragm was stretched.
There is plenty of water, the thermostat is working properly.
I have stripped the carburetor and checked the ports and jets and all appear in good condition.
It has new plugs and the gaps are set correctly.
Compression is good.
I've run out of ideas so any pointers or suggestions would be appreciated.
Thanks
Bob

 

[racerone]

Test run with another tank and hose.

 

[cymric]

I'm beginning to think it might be some kind of electrical problem.

 

[sgfrye]

I'm beginning to think it might be some kind of electrical problem.

any updates? my 1998 johnson 40hp has similar problem. after 5 trips to the lake i have pinpointed that it starts when fuel gets 1/2 tank or less.. its a 12 gallon tank.