Johnson Seahorse 4hp snJ4BRCNR water pump problem

" Hi,
I'm stumped, please

" Hi,
I'm stumped, please help.
Old outboard was given to me. Took it for a test run. Ran fine for a few minutes then stalled. Starter very hard to pull. Left motor to cool down for several hours. Started motor again but couldn't see any water coming out of anywhere. With some investigation, we realized that in fact, there is no facility to observe water comming out. Cooling water is pumped straight back into lower unit. I drilled 3mm hole in cooling channel just before the water discharges into the lower unit so that I could tell if water is pumping fine.

This worked well and now I can observe operation of cooling system.

Problem symptoms:
1. At lower to medium revs, water pumps fine.
BUT at high revs, water stops altogether and verocious air bubbling occurs around propeller.

2. With propeler shaft horizontal or pointing slightly upwards towards sky, water pumps fine.
BUT with propeler shaft pointing slightly downwards towards sand, water stops altogether.

3. When motoring boat straight forward or turning to port(i.e. motor pointing right), water pumps fine.
BUT when motoring boat to starboard(i.e. motor pointing left), water stops altogether.

Impeller seems new and undammaged. Intake screen not clogged. No obvious blockages.

Questions:
Could the combustion exhaust pressure at higher revs be high enough to force the water back through the cooling system?
What kind of water pumping pressure should I be expecting?
Do the symptoms indicate any water leakages between pump and discharge?
Could it be that at the higher revs, the water is pumping so fast that none exit at the hole I drilled?

Sorry for being so long winded.
Any help would be greatly aprreciated.
Thank you.
Iwan "

"Iwan..... That engine should

"Iwan..... That engine should have a few small holes, slots, a small water exit of some kind approximately half way down the exhaust housing (the housing between the powerhead and the lower unit), and all that should exit those holes would be a faint water spray (nothing great). The problem you're describing is that of a weak water pump, or a engine that is on a boat with a transom that is too high. The cavitation plate (the plate just above the propeller) should be approximately 1" below the bottom of the boat. If it is above the bottom of the boat, the prop will grab air and the w/pump will cease to operate. Let me know what you find.

Joe "

" Joe...Yep, the transom heigh

" Joe...Yep, the transom height causes the cavitation plate to be level with the bottom of the boat. No good. I have to do something about this.
However most of my tests are done in a bucket of deep water so I don't think the above will be the whole solution.
So, what can I do about the weak water pump? Do I need a new pump even tho' the one I have looks new anyway?
I'm really keen to fix this o/b so your continuing help is appreciated deeply.
Thank you
Iwan "

"Iwan.... Even if you were run

"Iwan.... Even if you were running the engine in a 50 gallon drum, you would encounter that problem. When you open the throttle, the water escapes the prop area very quickly. I'd suggest you forget the bucket scenario until you get the engine running right on the boat. The water pump may be perfectly okay but that remains to be seen (also wait until the boat/engine thing is straightened out...proper height). Pertaining to the water pump.... on any gasket, use a gasket type sealer that comes in a can that has a small brush attached to the underside of the screw off cap. On any metal, plastic, or "O" Ring seal area of the water pump that butts up against another material (no gasket), use a sealing substance in a tube called "Marprox Sealer 1000" You may find it under the original manufacturer name "Marprox" or under the "Boat Armor" label. The water pump surfaces must be sealed using sealer such as these or the pump would draw air into its system.

Joe (30+ Years With OMC)"

" Joe.. I hear what you're

" Joe.. I hear what you're saying but my tests are done with the prop removed or gear in neutral. However, I'll do the interface sealer thing and test on a more suitable boat.
Thank you and I'll get back to you on this.
Iwan "

" Hi Joe.. If you ever read th

" Hi Joe.. If you ever read this. Thank you. Thanks to your advice, I perservered and found a serious leak around the water pump which I glued up with RTV. "