I assume you changed oil and filter between runs, right ?

 If you give a little more info ( what engine, is it a jet ) maybe the experts will chime in.  Mine had a problem with the intake gaskets leaking water into the lifter valley but only at high RPM / pump preasure. It would run all day and be fine under 3500 rpm, but as soon as I opened it up = instant milkshake  !

Motor is a 454 punched to 468
roller
671
15lbs boost
jet

Yes, fresh oil
I checked the water pressure today, 15 psi at 23000 RPM. pressure came up quick with RPM. I'm sure it went way over 40 at 6000.

Plumbing is odd, pump to a T before the block, most water and pressure exits before the block, then through the block to another exit.

Should I add a valve after the first T ?
should I add the valve in place of the T first exit ?

Was your valley leak a gasket or a crack?

Thanks!

78PROPDUSTER nice name 

I'm curious as to how weird it's plumbed... 

Propless, is that the boat off of craigs list?

And is it a v-drive?

 No, I've had my jet boat for almost 8yrs now and my new project for the winter (21ft Eliminator/Daytona) is aaaa,weelll,itsss,kilda,aaaa,sort of an outboard  (propless hangs head in shame) but plans are being made to remove the cancerous growth back there and replace it with a proper motor and drive.

Hmmm V-drive, thats an idea.

No, not from Craigs list. Jet

Water comes from pump bowl to a T, one line exits boat, ( most water and pressure exits here )other goes into block. Then out of block to another exit. temp. runs 130 in the marina, drops to 100 once on plane.

Tested pressure, 15 psi at 2300 RPM. I'm sure it went over 40 at speed. I was told by a shop and long time boat wrench that it must have a valve to reduce pressure.

Said that blue printed pumps can run as much as 300 psi. My pump has been worked.

If you had a picture of the 1st T after the pump that would help.  I am guessing from your description that there is a pressure regulator here, hence the end of the T that exits the boat, if not well...  next while an auto runs less than 25psi on the high end I cant imagine that 40 would prove to be a problem if all the gaskets are holding the water as they should.  Jet boats were run with no pressure regulation for a long time before people decided to put regulators on them, that said most of us buy insurance for everything we own so my feeling on having one is that it couldn't hurt.  If I had to bet I'd guess it's leaking by a gasket somewhere, how long has the engine been together without a rebuild?

That's the same problem I had. I didn't know much about jets, and still don't for that matter , but I changed m head gaskets and intake gaskets and realized they were in fine condition. After doing some research I learned about needing a valve between the pump and the engine. I tried that and still had trouble so now I'm using the pressure relief. I've talked to some shops and they said the pump can put out 100+PSI, which an engine can't handle. And is your avatar your boat?

Here's a pic of it. The water from the pump goes through your valve, then into here... .once the pressure gets passed what you set it at, it dumps it back out the transom.

Rex marine has them, or HTP..... I think even some plumbing stores might have something

Ya thats my boat, havent ran it enough to mess with the wing. i'm running it without until I get the motor problems fixed. I wonder about the nozzle set up and want to make sure it is right. previous owner was not the original owner who raced it.
The guy I bought it from removed one of the two wedges which aim the nozzle up. I have to run the adjutable nozzle one click up from full down.

Did you ever have that boat on Craigslist? I KNOW i saw it on there a few months ago. Or at least it was a fake trying to scam money. I even found the thread I seen it on cause everyone was commenting about the wing, but by now that listing was gone

Sweeet