I need a little help please, 1999 Honda 9.9. On of my boys added diesel to the gas tank by mistake, said the mix ended up being about 75% diesel and 25% gas. The motor started OK and ran for about 2 minutes before dying, and would not restart. What the the best way to clean out the gas tank and motor, and what parts might need to be replaced?

That's a good one! You will need to clean out the fuel lines, including fuel pump, and carburetor completely. I would recommend a new fuel filter.
What I would do is first try draining the float bowl via the drain screw. After it has drained, leave the drain screw open, pull the fuel line off at the fuel fitting and **** compressed air through the line to **** the diesel out. You should see some more fluid trickle out of the float bowl drain. Reconnect the hose to the fuel fitting. Put a container under the float bowl drain and (after cleaning the tank and fuel hose out) flush fresh gas through that baby for awhile. I would flush at least a few cups through it to purge the diesel. The gas will just be flowing through and draining out the float bowl drain. When you're pretty sure it's flushed adequately, close the drain screw and start it!

If that doesn't do it, there may still be diesel in the carb. You might have to take the carb apart and clean it.