18hp seahorse. How do I

[razorback49]

tell what year it is. I am trying to figure out the correct oil mixture. It runs great on top end but low end chugs like a tractor.<br /><br />thanks,<br />bruce

 

[Paul Moir]

Re: 18hp seahorse. How do I

Welcome to Iboats, Bruce!<br /><br />Depending on the year, it's either 24:1 or 50:1. Go with 24:1 until you know it's age. It won't hurt the engine, just smokes a bit more. Use TC-W3 outboard oil and 87 octane gas.<br /><br />Check the port transom clamp for the nameplate with the model number on it. Failing that, look for a convex plug about the size of a quarter pressed into the block.<br /><br />Sounds like you've got the idle mixture set a little too rich, what happens when you lean it with the control on the carb?

 

[razorback49]

Re: 18hp seahorse. How do I

thanks for the reply. I have tried more rich and leaning it out with no difference. The plug you are talking about says 3867656. The spark plugs are jc6.<br /><br />thanks again,<br />bruce

 

[Paul Moir]

Re: 18hp seahorse. How do I

Spark plugs ought to be J6C or J4C depending on the year. JC6 is a lawn mower plug isn't it?<br /><br />I can't seem to get anywhere with that serial number, and you seem to be missing the model number. The serial number seems to indicated about 1973, but Johnson didn't produce an 18hp that year, just Evinrude. Can you describe the engine a bit? What colour it is, etc? A picture would be ideal.<br /><br />The fact that changing the mix screw doesn't seem to do much indicates a low speed fuel delivery issue. Try removing the knob from the control so you can turn it in further. It normally is about 1/2 to 1 turn out from turned in all the way.