1983 40-DT stalls at open throttle

[Professor]

Have a 1983 40-DT issue, runs fine at low and half throttle but stalls at full throttle. When testing with water muffs the water output quits at full throttle.
Have replaced the water pump and plate, but no change in the end result. Hot restarts there's no water flow at first, but cold restarts flow is immediate.
any ideas would be appreciated

[Solarman]

I am not sure I read you correctly? Are you running motor on muffs at full throttle? Really? At what rpm does it stall?

I don't understand what you're trying to see? Are you trying to see if water pump is working at full throttle?

A little shocked at this right now.
Post back when able.

[Professor]

Let me restate it, Trying to replicate water pump apparently cutting out on the lake at open throttle which coincided with the motor killing shortly afterward.
Did not have a tach on it then and don't have one to check at what rpm it dies at

[Solarman]

If water pump impeller assy is good, you might be having a problem with exhaust getting into water pump chamber. Exhaust pressures at higher rpm's can interfere with the water pumps ability to push water through the motor to cool it down. This could trigger a overheat shutdown?

This could be occurring in the lower midsection near the water pump (if the aluminum webbing, chamber, or grommet(s) is/are deteriorated and allowing exhaust into water pump chamber).
Also may be occurring at the exhaust manifold on the side of the powerhead (if any bolts are missing, or any of the water pas-sages are deteriorated, allowing exhaust into the water side).
Or possibly under the powerhead where it bolts too the midsection, as well as the midsection itself.

Most of these areas if deteriorated can be welded back up by an aluminum welder, then shaped by grinding. The problem is, finding where the exhaust is getting into the water system.

Good luck.