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73 Johnson 20HP no run

K

Kluth

New member
Hey guys, got my first boat motor it’s a 1973 Johnson seahorse 20Hp. It currently doesnt run and I’m at a stand still. It has spark, fuel, and compression but still no run not even a sputter. Compression was a bit low at 72psi on both cylinders not sure if thats too low or not. Not sure if I'm doing something wrong when trying to start either lol. I am currently using 32:1 ratio left over from MX season not sure if that would be too rich and cause it not to run. Im used to two stroke dirtbike motors not sure how much different they are lol. Anything helps thank you guys in advance!
 
Kluth,
How long has this engine been sitting? Start with the easy stuff, 72 psi on both cylinders is low, should be around 120, try another gage. Even psi is good. Does it have spark on the plugs while grounded on the block?, does the gearcase have water in it? Once you answer these basic questions we can take the deeper dive into details.
 
fitz73222 said:
Kluth,
How long has this engine been sitting? Start with the easy stuff, 72 psi on both cylinders is low, should be around 120, try another gage. Even psi is good. Does it have spark on the plugs while grounded on the block?, does the gearcase have water in it? Once you answer these basic questions we can take the deeper dive into details.
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Other gauge read around 70 as well. Yes good spark with plug grounded to the block. Gear case had a little bit of water in it but mainly oil. Planning on checking gear case more in depth once it’s running. Whats a good place to diagnose the low compression. I know the normal culprit on dirtbikes is piston rings
 
Excellent news! Check for a thermostat while you're at it and order those parts as necessary. I'd be careful with motocross oil. Not sure how it's rated. You should be using TC-W3 oil , 3 oz. per gallon (50-1)
 
fitz73222 said:
Excellent news! Check for a thermostat while you're at it and order those parts as necessary. I'd be careful with motocross oil. Not sure how it's rated. You should be using TC-W3 oil , 3 oz. per gallon (50-1)
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10-4, ill swap out the fuel and take a look at the thermostat. Head gasket is set to come in today!
 
Your cylinder head is warped.----Needs to be refinished ( flat / trued up ) before installing the new head gasket.
 
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