Decarbing might help?

[PatinIdaho]

Pappy » 29 Aug 2014, 15:22[/url]"]That engine should probably be around 750-800 RPM in gear at idle at this stage of its service life.

So Pappy, After reading several of your posts over the last few months I have grown to respect your opinion so im going to ask you directly.
Im pretty mechanically inclined. I grew up in the Auto/Semi repair business and now in the aircraft repair (Mechanic) and after taking a close look at it I believe rebuilding this engine is well within my capabilities so with that said.

How far do you think it would be feasible to go with this engine work/money wise?
Would you just run the piss outta it till it died and find another sub $1000 engine? Or fix it up and keep it?

I can't afford a new engine and probably never will. I could sell this one but the next one might have problems also that do not show up right away like this one.

Just rings and gaskets are about $300ish with $100 for odds and ends so $400 total or very close to it
New oversize pistons(rings included with pistons) and gaskets are close to $500 Having it bored probably $100ish so roughly $600 with the little few pieces not mentioned im thinking a total of $700 and if I needed all new bearings that's another $150ish
With just rings I think it would be good for 3 or 4 years at least
With a major rebuild I think it should last about the rest of my life(im 52)
The engine is actually in really good shape and does not show its age. Paint is still bright and shiny. Lower unit works properly and the oil in it is clean.
It has a new Stator and Switch box. Stickers are a little rough but with new stickers it would look almost new.

 

[Pappy]

Have watched this thread to see which way it was going to go.
Your earlier comment/question on how low can compression go before you cant get the fuel air charge to the top of the piston was right on, hence the reply.
A two stroke engine has to have two kinds of compression to idle well.
It has to have the measured compression we see above the rings and it also has to have adequate crankcase compression/vacuum below the rings to pull in and push or accelerate the fuel charge through the crankcase and over the top of the piston.
Piston and cylinder wear in a two stroke is similar (in most cases) to that you would see in your profession in that the piston skirts will wear at a higher rate than above the piston ring.
The cylinder will also wear more down in the skirt area than at the top of the cylinder giving you a measurable taper.
This type of wear translates into a weaker than normal crankcase compression ratio which can and will result in the scenario you were thinking about.
Your choice in rebuilding would be to over bore and use new pistons and rings, not re-ring.
Having said this I would definitely raise your idle rpm way before going to the trouble and expense of a rebuild.
Am not as familiar with that particular engine as I am the Johnson and Evinrude brands but have been around them. Have seen this scenario several times in the 2 & 3 cylinder loop charged engines that OMC manufactured. Top compression would be great but the engine would just "go to sleep" at an idle in gear in the water.
Band-aids are to raise the idle, richen the mixture and advance the timing to buy some time.
In your case I think simply raising the idle RPM will help quite a lot since a 650 RPM in neutral would most likely translate into a 500 RPM in gear number...too low.
BTW - My Dad had his "A&E" license issued to him back in the 1940s and I got my "A&P" license in 1972 while going to college in Daytona for Pilots licenses and Aeronautical Sciences.

 

[Pappy]

...on the subject of "De-carboning"
Have seen all kinds of responses on here about what to use and how to do it.
If you want to do it right get a manufacturers brand first off. They are more powerful.
Second. Bring the engine to temp and on an engine like yours use at least over a half can to as much as a full can. Keep the engine
running at a high enough idle to not die. It should be running pig rich and barely running while you are using it. Neighbors should think
your house is on fire with as much smoke as it will produce......
Once almost done with the can drown the engine with it, do not let the engine clear out.
Let the engine sit anywhere between 3-16 hours minimum. I do overnight as a rule. Let the chemical work!
Start the engine and let it sit at a dead idle for at least 15 minutes to clear carbon chunks out. This stuff can scuff the bore as it is
being released so idle only for a while. Add oil to your mixture in a tank you run the engine on to keep the bore as protected as possible after a de carbon job.

 

[PatinIdaho]

Thanks Pappy.
Im leaning towards a complete rebuild.
For the money I don't think I can find a better deal then I would end up with if I do a major overhaul.
Other then a unknown fatigue issue a engine that is rebuilt should last just as long as a new engine in my experience but 2 strokes outboards are new territory for me! so I guess I have been leaning that way from the start just afraid to admit it #-o
In a couple months I will be putting it away for 5-6 months(winter) so ill have plenty of time to do it.

 

[Pappy]

Well....in the mean time give the engine around an 800 RPM in-gear idle and see what happens.