Engine break in question...

[suprajake]

Ok, so I recently rebuilt my engine, cylinders up. Took it out and ran it, like suggested, with premix gas and no more than 50% or so throttle for the first hour. During that hour I would drop to idle and feel the engine right on the top, feeling for heat. The first 50 minutes it stayed about the same, no excessive heat on the engine, I could have my hand flat on it. The last 10 or so minutes it started heating up just a little bit. My question is this. When the engine heats up is it better to run it lower or higher RPM? I can see arguments for both, as lower is less heat buildup but less water movement, and higher is more water movement. I just want to keep breaking in this engine a little more before I start revving it up. I did bring it to about 100% a couple times just to plane out before backing it off, which I read is ok, just a matter of I was wondering what's better for heat dissipation right now. Thank you!

 

[seadooya]

ur good, if anything, recheck the cooling lines, blow air thru them. but ur "philosophy", gotta agree with, no impellor movement, no water movement.

 

[suprajake]

I'll definately check the cooling lines, I know it's getting a ton of cooling as I could put my hand on the exhaust and feel cold after an hour, so that part was good, just the top of the engine heated up to the point I couldn't comfortably hold my hand on it anymore. Not comfortably anyways. Still not bad for an hour + of constant running, no break other than going to idle every 5-10 minutes for a minute or 2.

 

[seadooya]

check the waterline from the bottom of cylinders, how it goes to the back, where the exhaust flange is, make sure that line is clear.

 

[suprajake]

Will do, thank you for the direction! At least now I know where to look to find any potential problems

 

[suprajake]

Now I have another question. What would make the plugs burn un-evenly? After running the boat just over an hour on the lake, I pulled the plugs at home and this is how they looked. The clean one was from the rear cylinder, the dirty one was from the front. The clean one looked like it hadn't been burning at all, or very little if any. They're both full of oil, which I expected, as I'm running a hefty premix for engine break-in. Compression test on both cylinders, 148 and 149.

 

[suprajake]

Can anyone answer the plugs question? I'm planning on running new plugs tomorrow when we go out but I just want to know if there's something to look out for, or if maybe the carb just needs to be rebuilt. I'm hoping to rebuild it this winter, can I make it till then?

 

[Dr Honda]

The PTO plug will normally run a little hotter. (and cleaner) At this stage of the game... Since your electrode is dark, I wouldn't get to worried if it seems to be running well.

If it were my boat, I would open the PTO high needle a 1/4 turn, and continue to break in the engine, and monitor that plug.

 

[suprajake]

Hm... Where is that needle? Been far too long since working on a carbeuretor, and even at that it was on a car :blush: