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Last summer I bored out and rebuilt my 1996 Johnson 70hp 2 stroke motor. I am taking it on its maiden voyage this afternoon. Other than my ears, watching the tell tail and taking temperature of the head while it is running, what should I look out for? I am going to follow the break-in instructions in the shop manual, but I am not sure what to watch or look out for. I am running double oil as recommended by the manual. My outboard oil is synthetic, should I find some "regular" oil to "break-in" the rings?

Chris

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Well, the first thing I can say to watch for is to make sure your thermostat is installed properly. Best I can tell I was shipped the wrong thermostat and the engine was overheating after a few minutes of operation. I stopped home at a repair shop and he told me to look at the thermostat. I went home, pulled the themostat and ran it on muffs, AMAZING. The tell tail went from hormoned-up teenage to oh my prostate, I can't pee.

I will order a new thermostat and see how she runs.

Chris

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The accessories.

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I would talk a little further with your mechanic. Seems to know what he's doing.

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After any major rework of an engine I do a shake down run without passengers or distraction. Listening and watching for any sign of problems. Check plug colour a 1/2 hour into the trip and again after. Bring a spare set in case that double oil mix fouls your plugs on idle.
I've read that dino oil is better for break in (in a 4 stroke), but the reasons were "too complicated to explain". I'm not certain that opinion would even translate to a 2 stroke application since the oil is burned and puffed out the exhaust. To me, good oil is good oil.
Did you use new head bolts? Checking head bolt torque after a few trips was also part of the drill.

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Yes, this guy was very knowledgeable. He was positive it was my thermostat and nothing else. I am going to take it for a ride this weekend without the thermostat installed and see what temps I see.

I already have 2 sets of extra plugs, as you said they get fouled quickly.

I checked the compression and I have almost exactly 125 PSI in each cylinder.

Tig, I agree with you, I took a half day from work so I could run this in peace and quiet! It was a little scary to hear and see steam leaking from the tell tail.

I used the same head bolts, and the manual states to retest torque at the end of the break-in cycle.

Chris

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Success today, removing the thermostat the engine ran great! Never went over 110 degrees, which is actually probably too cool. I got 2 hours of run time on the motor today and fouled a set of plugs from the double oil it seems.

I have a new problem, even with brand new plugs it will idle for a short while, decrease in speed and finally die. This takes a minute or so. I have the idle timing screw probably 1/4" from being screwed in all the way. To me it feels like a fuel delivery issue, what should I be looking for? I am going to proactively replace the fuel line to see if that addresses the issue.

Chris

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I'd suggest getting the correct thermostat in and running the rest of the break in (and then some if you've already logged a number of hours w/o the thermostat) at proper temp, then see how it idles at that point.

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I ordered the correct thermostat last week, I think I will hold off troubleshooting until I get that replaced.

I have around 4 hours of run-time on it, so I think I am through the most critical part of the break-in. I am also going to stop adding the extra oil to the gas.

Chris