wont start in water

i recently acquired a "new to me" 1972 johnson 50 HP. this is one of the electric shifts. I bought it from a local dealer here who had taken it in on trade a while back. Sold it to me as-is, however he had looked it over, said the compression was good, pressure tested, and i paid a little extra to have the carbs cleaned and rebuilt.

I have had the boat out a few times, and it works/worked great. However a couple days ago i ran the motor into the ground/mud at low speed. this resulted in the motor shutting off, while there i was able to get the motor started very briefly, it didnt sound like it was running particularly great, and the moment i attempted to put into gear it would shut off. Since then i've had it running in my backyard on muffs, seems ok, shifted it into and out of gear a couple times, seems to work fine. and i started it up in a barrel, i will say it seemed rough in the barrel.

Today i brought it out to the lake and had the motor in the water and it wouldn't start, it sounded like it wanted to. i tilted it up until the back of the prop was out of the water, it did start, and i lowered it back into the water where it ran very roughly for maybe 30 seconds or so, before shutting off again.

I'm not all that familiar with how to work on these, but i dont mind trying. is there anything obvious i should be looking at or checking?

Some will argue----The first thing I would do based on the information presented in post #1 is a compression test !----Perhaps check for a sheared flywheel key too.-----Note-----No money spent so far on this inspection / testing !

It's hard to believe the mud had anything to do with it unless you got it so plugged up that it overheated to the point of destruction. Nevertheless, I agree, a compression test should be #1 on the list. Only after it passes that, continue with the ususal trouble shooting items, spark, fuel, etc checks. Could be as simple as manual choke position or fouled spark plug. Don't freak out and fix something that isn't broke.

did the compression check, got 145 up top, 140 on the bottom. as for the sheared key idea, i did a limited amount of searching on the web, and that sounds like it might be pretty involved? or is there less to it than im thinking?

Not to deny the possibility of a sheared key, but in reality, that would be pretty rare unless somebody had it apart and reassembled it wrong. You need a flywheel puller to get it apart and you MUST use a torque wrench to tighten the nut to spec., which is 100-105 foot/lbs

Edit.....

Did the hot alarm sound???

no, no alarm sounded.

can anyone tell me what size bolts i need for that puller? i thought i had the right answer, but they were too small.

Threads in the flywheel are 5/16-NF -----or 5/16"- fine thread.

edited

so im not 100% sure what the flywheel key should look like if its in good condition, but im thinking this looks good. anyone care to confirm or deny that for me?

Tis good..remove it, apply some fine valve lapping compound to shaft and lap shaft to flywheel. Clean and reassemble. Need to test alarm horn to se if it work.

So i read another thread that gave some brief instructions on testing the horn, if i understood correctly, on this wire i have an image of i pulled the rubber back, and rubbed the silver connector against a couple of the bolts in the background while the key was in the run position? anyway i did that and nothing happened.



I am wondering, obviously a couple of people have suggested in this direction that maybe the motor overheated causing further damage, but i was under the impression the numbers from the compression test excluded that possibility?

If horn failed to sound it likely bad....that model 50 has domed pistons and compression runs high. Compression test means cylinder will support combustion but does not mean there is no damage. I see this problem with these models all the time as crankcase halves leakage and worn/scuffed skirts on piston. Reason it wont start in water is backpressure is higher than crankcase pressure and cannot force the fuel/air mix into cylinders. It will start and run on muffs with no problems

So if what your suggesting is correct, this would sound like a fairly major repair? would it be worth fixing? If i happened to have the same year and HP evinrude version of this motor laying around, would it be worth it to have a shop swap that part in?

The EVINRUDE had different color of paint.----So the parts are the same.

If i happened to have the same year and HP evinrude version of this motor laying around, would it be worth it to have a shop swap that part in?​

Click to expand...

Only if it ran with no problems...