I wish my boat was as light as those surf boards    It would probably have
been fine with the Victor.

Very nice!

One other thing on the depth of water you run in.   When your boat is loaded it digs deeper when you take off.   Mine pulling 4 skiers seemed like it blew a hole about 6' deep behind us when we started out WFO.

So, don't be in 5 feet of water with a full boat and nail it.  My boat is 23' and I would bet it digs deeper than a 16 footer but I do think it's something to be aware of.

Welcome to the club 

Thank you, I'll give it a try.   I'll probably use a 1" spacer though.... it will be through the sun
deck with 2 

You will only read the 12.53 with an OPEN circuit.  If it were draining you would read the voltage drop across that resistance.
It's miller time   

WRONG!

Marine head gaskets are not just for salt use....Marine engines do not have the advantage of the anti corrosion protection of anti freeze. Thus making the electrolytic effects of brackish waters left in an engine most detrimental to the survival of the sealing surfaces...

I use brass freeze plugs and marine head gaskets in all boat engines. Cheap insurance IMHO...

A trait that marine gaskets also have is dielectric bonding of the sealing surfaces, this is like a good primer on bare metal on a paint job, it keeps the free iron from being exposed to the gaskets metal, which is how they function to begin with.

This has been a major debate among the boating community for decades, it is my opinion that the only time "standard" gaskets should be used is when the engine is not expected to be together for more than 6 months (read; full race deal)...

Sorry for the harsh intro, I feel strongly about this because I have taken apart literally dozens of engines that could not be salvaged because of the amount of corrosion in the sealing surfaces of the heads and block...

GT

While I admire your strong opinion I must say I don't fully agree.  I pulled apart a  460 jet after 6 years of use with the felpro gaskets and they were absolutly fine.   Fresh water use in a clean lake.  So yes use the marine gaskets if you want.   But I sure wouldn't worry myself to death about it if I didn't is all I'm saying.
I'd be taking a hard look at that deck job and make darn sure it's square.   Did you chase the threads before you
put your heads on???  I think there is more happening here than water pressure.

Was that gps or water speedo?  My 23' ran in the 50's with 4 people ice chest etc, when it was stock.

Oh, that was a Ford engine     

I would think it should go quicker than 49 with a 21" boat.  With a water speedo you're just
taking a good guess anyway. 

The problem with the center risers is that they don't clear tall valve covers.   I'd rather have the
solid valve train than the center riser.    They might cost me a little flow but I won't have to
paddle home 

I have to wonder in the 5,000 rpm range how much logs and center risers cost in HP.   I know I'd really
be worried if we were talking 6500 + rpm's,  No not worried PANICED!

It would be nice to know flow numbers for the different brand logs and center riser manifolds.  I never read of any testing done. 

Sounds like you nailed it.  Bad pump.  I'll let the guys running electric take over from here.

I never liked the idea of an electric pump, more likely to fail.  If ya don't need it I wouldn't
use it.
JMO

Welcome to my world     You are in the same boat so to speak as me. 
Headers needed, enclosed engine compartment restricted and money short 

I'll be watching this post to see if anyone has figured out great flow without
burning up the boat 

Another possibility is the old fuel line to the pump.   If the hose gets old and weak the pump could be
sucking it shut under hard load.  I had that happen once... I change my hoses every couple years now.

What carb?  Sounds to me like you don't have enough accelerator pump squirt 

Never heard of it?  Where do you get it?