1963 Johnson RK-25 40 HP Electramatic won’t start

[oldboat1]

Measure the spark and post results. Issue is not likely the plug, it's the ignition output/strength:

 

[racerone]

Checked fuel pump diaphragm ?

 

[jimmbo]

That engine has a recirculating cooling system. Until the stat opens the vast majority of the water is returned to the waterpump
As for why it might be running hot...
Clogged cooling passages
worn water pump(there are other parts that wear out besides the Impeller)
Incorrect ignition timing
Lean carburation
Wrong spark plugs
Wrong oil or wrong mixture
Exhaust is getting into the cooling system, instead of the reverse

 

[McJuice]

Thanks for everyone’s input. I greatly appreciate it! I think DH is in over his head. I have convinced him to call in a professional.

But I do have another question. Would this 1961 75 Horse power Johnson (VA4L-13) have any parts value for our motor? He’s asking only $75. Here is what seller said about why he’s selling it as a “parts” motor...”It turns over, but can’t get it to Turn over fast enough to do a compression check”.

 

[McJuice]

Correct me if I’m wrong, but I didn’t think the engine was supposed to turn over during a compression test?

 

[oldboat1]

semantics. Spinning the motor without starting is usually called "cranking". And it has to crank somewhere around 200rpm to fire (pretty fast). Usually a problem with the battery or connections if cranking too slowly, sometimes the starter.

 

[racerone]

Of course the motor has to turn for a compression test !!----That can be done with the recoil on that 75 HP motor.-----The sparkplugs and some nuts and bolts can be used for your 40 as spare parts.----Nothing else is comparable

 

[oldboat1]

Plugs out. Pull it over until needle stops. Record result.