Assuming that the water inlet screen is not choked; this engine has a flush
attachment hole on the underside of the powerhead.
Remove the largest diameter bolt on the underside of the powerhead and run
the engine briefly.
If water pumps out of this hole then the impeller is probably OK and the
tell-tale hole is probably blocked.

If water doesn't pump then........

Prise off the rubber bung on side of the leg.
Put into either forward or reverse ( I can't remember which) until you can
access the gear shift clamp screw through the hole in the leg.
Slacken the clamp.
Remove the 2 bolts holding on the gearbox.
Give the gearbox a dunt downwards.
Remove the gearbox.
Remove the bolts holding down the water pump cover.
Remove the impeller - (don't lose the tiny woodruff key)
Replace the impeller and gaskets and re-assemble

Regards

Allan




"Peter Eichler" wrote in message
...
Dear all,

I have a Mercury 4 hp 2-stroke, assumed to be from 1990, which has a
problem since I used it for a longer trip on my 17 ft sailboat.
After having run for a couple of hours the tell tale flow became quite
weak, the engine still ran but the temperature seemed to become somewhat
higher than normally when I use it just to get out or in the harbour. I
tried to suck on the tell tale hose and there was a high resistance to
get some water through it.

My assumption is that there is an issue with the impeller. Is there
anybody experienced enough to describe the impeller replacement
procedure or even can provide a kind of maintenance or repair manual?

Any help is highly appreciated.

Regards,

Peter