1973 Johson 50 HP

[aaromba]

Hi guys I got a 1973 johnson 50 HP 2 cylinder. Does anyone know what the compression is suppose to be? I have 80 PSI in one and 90 PSI in the other. I was thinking a blown head gasket reason being. Water pump was getting bad I changed it, then motor overheated, I then changed thermostat and relief valve I am not sure if its another bad thermostat? Doesnt seem to overheat everytime, so I thought maybe a blown head gasket?? The other day the water was warm coming out of the outlet today it was cold overheat alarm went off?? Anything would help thanks!!

 

[tashasdaddy]

Re: 1973 Johson 50 HP

i would want to see 100 plus, more importantly, with in 10 % of eah other.

decarb may bring compression up. if you ran the motor with out a water source.

did you blow out the water tube when you had lower off?

could be head gasket, but i am not betting on it.

salt water or fresh water motor????

 

[bktheking]

Re: 1973 Johson 50 HP

If you had a blown head gasket you'd have almost no compression, do a decarb to start.

 

[aaromba]

Re: 1973 Johson 50 HP

Yes I did blow out tube I am in fresh water. I am thinking of trying another thermostat, what do you think? I am running out of things!

 

[aaromba]

Re: 1973 Johson 50 HP

Sorry I dont know what a decarb is?

 

[tashasdaddy]

Re: 1973 Johson 50 HP

Decarb

i would do a decarb, then if it did not come up, the head gasket.
Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck

 

[F_R]

Re: 1973 Johson 50 HP

You said it overheated after you replaced the water pump. Now the compression is low. Sorry, but the way I read it, something is messed up with the water pump job. Now that it has overheated, something is really messed up. Or shall we say burned up?

 

[aaromba]

Re: 1973 Johson 50 HP

Can you tell me what the relief valve above the thermostat is for? I am guessing to let water circulate out until the thermostat opens. And how does it go in spring first or relief valve then spring. Thanks for the decarb info. I have dropped the lower end and looked at the water pump everything looks good. Thanks for all the info you guys have been giving me!!