1979 90hp mercury inline 6. Will idle & go 5mph all day @ WOT it will run 5 mins then stall?

Question

I have replaced all fuell lines. checked elec. all seems fine.

Answer 1

that motor has a heat switch that sounds an overheat alarm, but unless you've modified it in some way, it doesn't shut the engine off.

If it's really shutting down due to overtemp, it's seizing.

It's not unlikely that your switchbox could malfunction when things heat up under the cowl.  This can be determined by checking for spark after it shuts down.  remove a spark plug, reattach it to the boot, hold it against the engine block and look for a sharp blue spark while an accompliss turns the engine over with the key.

Try squeezing the primer bulb when it starts to die, if that makes it run, then rebuild the fuel pump.

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"I have replaced the Water pump, rectifier ( some bad elec. conections), & all fuel lines. After it dies it will take at least 5 mins before it cranks after it cranks you can kill it then bump the key and every time it will fire off. Im thinking switch box.??"

sure it might be the switchbox.  if you just want to randomly throw parts at it hoping to get lucky, then buy a new one and see what happens.

On the other hand, if you'd rather not replace parts that aren't broken, do a little troubleshooting as described above.

your call.

Answer 2

WOT  will prevent water going in engine to cool it...the sensor ''sees''' the heat and shuts down the engine.. KABISH ??