Water Pressure dropping

[TownsendsFJR1300]

I replaced the small o-ring on the inside of the pump as the old one didn't fill the gap properly.

An o-ring, along with any other seals do make a difference. A very slightly warped housing will also guarantee water flow issues. And that's on a boat that has the engine plenty deep enough on the transom (as yours seems to be right at the limit, maybe high).

Every little bit helps in your case...

Re water coming out when putting water IN the water OUTLET, the exhaust of course, comes out thru the prop. The water is just bleeding out (with it NOT being attached to the lower leg). That has to be water cooled or it'll cook the prop insert. I suspect that's why water's coming out there.
Not sure if that makes sense(does to me!)..

You likely have some larger o-rings on the ends of the water tube that goes from the LU to the power head. I'd peek at those as well if not too hard to access..

[ThaiWake]

The water isn't leaking out the prop shaft, it is leaking out the drive shaft. The shaft that comes out the water pump and connects to the upper unit of the engine.

I put the hose in the outlet of the water pump and there is water leaking out the housing of the water pump through the drive shaft.

I don't think this is normal, if water can get out that means that air can get in, could the water pump be sucking air in through the drive shaft??

I thought that when I stuck a hose in to the water outlet water would leak out of the water inlet screens, the prop and the exhaust, I didn't expect to see water coming out through the drive shaft?

[99yam40]

It is normal for water to come out around the drive shaft as there is not a tight seal around the shaft. If there was a tight seal, it would heat up from the friction of the shaft turning fast at high RPMs.

For it to come out of the intake screens it would have to get past the impeller, and that is suppose to be sealing to the cup and wear plate

[zenoahphobic]

It is normal for water to come out around the drive shaft as there is not a tight seal around the shaft. If there was a tight seal, it would heat up from the friction of the shaft turning fast at high RPMs.

For it to come out of the intake screens it would have to get past the impeller, and that is suppose to be sealing to the cup and wear plate

I guess one can think, just because the tap hose pushes water out of the top of the pump housing around the driveshaft, that when the engine is running the pump would do the same.
Not so as it is submerged- some water pressure on the outside, at least at idle. But more importantly the pump has centrifugal function (as well as displacement), that forces the water away from the centre.
That said I can't see why this fandangle pump can't be provided with a proper seal. This design fools just about everyone that looks at these pumps for the first time.
Not as if Yamaha can't make decent pump; no such confusion with their water cooled motorcycles.

[ThaiWake]

Just back from the water after putting the boat back in and so far so good, did a few tests and the cooling system seems to be working again.

The bad news is I can't say exactly what fixed the problem, it could have been the fresh bottom paint, it could have been the new o-rings or there was one other thing I noticed on the water pump housing, there is a small hole in the top of the housing, I guess this is an air vent, this was blocked with dirt so maybe air was getting trapped in the housing?

Anyway, cleared this out and so far everything seems good. Glad to be back on the water but still a little puzzled as to exactly what the problem was.

[TownsendsFJR1300]

Congrates and thanks for the update!