'73 Evinrude 115 - A lot of smoke!

[BOAH]

Took my '73 Evinrude 115 out for the first time today. It really ran well but I noticed a lot of exhaust smoke and the smell of gas every now and then. I rebuilt the carbs three years ago and am wondering if it's time to do it again. Or should I try some adjustments? Not sure what I should do at this point.

Your input is always appreciated!

 

[emdsapmgr]

Re: '73 Evinrude 115 - A lot of smoke!

If an engine is running cold, it will smoke more. Check to see if the engine is coming up to normal operating temps at idle. There is an airbox drain hose at the bottom of the airbox. It recirculates excess fuel from the front of the carbs (minor drips, etc) back into the bottom cylinder for combustion. If that hose is missing or not connected this small amount of fuel can leak into the lower cowling.

 

[BOAH]

Re: '73 Evinrude 115 - A lot of smoke!

That hose appears to be connected. Hard to check the connection where it feeds back into the motor because it's underneath the carbs. I ran the motor for probably 2 hours yesterday so it was definitely up to operating temperature. It was better when it warmed up but if I shut it down and restarted, the smoke was bad and when I was loading it at the end, it was definitely visible.

 

[metriccrescentwrench]

Re: '73 Evinrude 115 - A lot of smoke!

... I ran the motor for probably 2 hours yesterday so it was definitely up to operating temperature.

Not if you have a bad thermostat, or worse yet a missing thermostat. At idle the head should be around 140 deg F (at least that's the spec for the engines I've had), at that temperature you should be able to hold your hand on the head for maybe 5 to 10 seconds before it feels too hot to touch. If the head feels cool to only lukewarm after several minutes of idling then the engine's not getting up to temperature.

 

[emdsapmgr]

Re: '73 Evinrude 115 - A lot of smoke!

I believe the single vernatherm (thermostat) units run cooler than the later units with the dual stats. The 73 stats open somewhere around 115 degrees.

 

[BOAH]

Re: '73 Evinrude 115 - A lot of smoke!

This would make sense to replace the thermostat since I've never done it. Looking at a parts diagram for this, the part I need is called the vernatherm? Is there anything else that I need when I do this for this motor? (1973 Evinrude 115 Model #115393M) I called iBoats for this but they said they don't list it for this motor??

Is there anything that I should do when I replace it such as try to flush it? Any good instructions on how to do this job?

Thanks for your help on this!

 

[emdsapmgr]

Re: '73 Evinrude 115 - A lot of smoke!

You will probably want to replace the gaskets involved. There are some while, nylon parts inside-valves. You'll want to examine them to be sure they are not deformed from an overheat. If they look ok, reuse them. An original factory service manual is the best reference. See this website: outboardbooks.com Also the factory parts website: epc.brp.com