While on muffs I can take the hose off the back of the pump turn the hose on and nothing.
Remove hose from dual feed muffs and put the water down the sea inlet hose and it pours out the muffs no problem almost full flow of the hose.
This is Bravo One set up with 454.

Could not get the water to run through the system and don't want to waste pumps.

If I am understanding your post correctly Its normal. I might be lost what you are saying and trying to do here. My thoughts are not clear about your post and what you are trying to do

Thinking if this is what you are asking - That's why marine engines have a sea water housing and impeller to pull water up and thru to the engine / t stat housing sides and exhaust system. The engine has to be running for a working rotation of the impeller. Turning water on with muffs and no working impeller it not go to pull water up and thru the drive and or water pick up(s). You need the suction of a working impeller to do that job PULL water thru the drive water inlets or external water pick up(s) however the boat is set up. Hence why they are installed to do so.

How new is this boat to you ???

Just in case I am not following along correctly - do you have a water inlet / pick up under the hull like a inboard ski boat and inboard cruiser type boats have ???

Or do you have your sea water pump hoses connected backwards ???

The hose is off of the pump and water will not flow to it.

The hose to the pump is off and water will not flow to it.
All was fine when I ran it a month ago.

What led you to discover this?
You are saying from the muffs nothing , but if you put the garden hose to the inlet line it flows fine back out the outdrive intakes.

Does the water run out of the exhaust when the motor is running.
As was asked earlier, what caused you to look for this?

Yes Buck
When I fired it up, I had nothing coming out of the exhaust.
Cracked a couple of hoses loose to make sure it was not an air lock.
It is like there is a check valve going to the pump. The only explanation is a very weird piece of impeller is stuck. Pulling out drive off this morning and see what the hell it is.
What a waste, sunshine and dead calm for once here in Kansas this morning.

Take the hose off at the transom assembly and check it for internal failure. The one that feeds the pump.

Doing that. That is the only place that this can be besides in the outdrive itself.
The hose is like new, but you never know. Missing some great boating, but that would not be the first time that happed to someone....lol

Well, took off the drive and have full flow at the transom hose to the pump.
Put the muffs on the drive laying on it's side and several pieces of impeller came out.
Does not make any sense what so ever, but going to go put it back together now and see what happens.
Bette throw another new pump on just in case.
Lucky I had 3 extras that were for my 38 Special.