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1976 15hp Johnson Water pump Question ???

R

rebranger

Member
I have a 1976 15 horsepower Johnson, Model no. 15R76A, pull start. It doesn't have a "pee line" or water pumping indicator line. I rebuilt the carb, put in new points & condensor, cleaned the fuel pump screen. This motor had been submerged in fresh swamp water for about a month. Pistons were siezed, but weeks of soaking with KROI oil got it aloose. It now runs fine but I think it may be running hot.
I ran it with standard earmuffs & later in a tank. I could not hold my hand or finger on head or freeze plug for very long. Paint is not discolored.
How do I tell if pump is pumping?
How to overhaul pump?
Where is the shift rod disconnection? i.e., How do I disconnect the shift rod?
My other johnson, ,1978 20, 1981 35, & 1981 88 SPl all have a cover plate. This one does not.
ANy & all help appreciated!
Thanks
 
To change the impeller you will put the motor in forward gear, remove the six bolts where the LU connects to the mid-section. Let the LU drop down about 1 inch. In there is a brass slotted screw that needs to be removed to disconnect the shift rod.

This motor has an exhaust relief hole just under the head on the back where water should exit when the water pump is pumping. It usually will take about 15 seconds after start up to see a small mist of water as it waits for the T-stat to open somewhat. You should always use a barrel of water as opposed to muffs since for some reason water does not always come out the exhaust relief when on muffs. Don't really know why.

I would change the impeller and see how it works after that. Make sure the water in your barrel is at least 3 inches above where those 6 bolts are for the LU, to ensure the pump is primed.

If that doesn't fix your problem, then perhaps the upper water tube grommet needs replacement. That is a lot more work since the powerhead needs to be removed for access.
 
If you take the thermostat out, be sure to replace it. These little motors run best when they run at the right temperature. If you're scorching the paint on the powerhead, the FIRST thing I would do is check the pump impeller. Thats the heart of the cooling system. Is it spitting water out of the exhaust relief hole at all? Once it's warmed up, it should be spitting water out of that hole at a constant cadence. If its not, you've got a bad impeller, or a restriction somewhere.
 
The thermostat is at the bottom of the head, behind a cover that covers the front of the head. You can take the latch out to get to the bottom couple bolts. Those are the ones that are a pain. Another thing I'be done with stuck thermos if they're corroded is dunk it in some CLR and let it eat the corrosion away. I've done this several times when they get corroded shut with that white flaky corrosion.
 
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