Rich is a spectrum. 99% of people that have a rich engine have carbon fouling. The rich you’re referring to is so rich that it will hardly run, not just on the rich side..
Oil VS Fuel
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Excessive carbon build up on the crown in most cases is caused by running lean. Excessive carbon in the exhaust port and muffler is typicaly caused by running rich.
A piston that shows a bare metal crown has either not been run long or is running very rich/cool.
A perfectly tuned two cycle using quality oil will have a piston that is covered in a thin layer of carbon with small spots of bare metal wash where the ports discharge.
It's not normal to have a bare metal piston at all. If you were expiereanced you would know this.
This is a crappy photo through the Spark plug hole but you can make out the transfer wash and the carbon on the piston. This is from a Redmax 3050 trimmer with a GXZ30N motor my son uses in his lawn care business. It has used Red Armor and Alkylate fuel since new. It's also tuned bang on.
Here is a pic of a piston with nice symmetrical port flow and tuned bang on for peak performance. Notice the carbon present shows no ash deposits. A well tuned engine ran on decent oil.
Not my pic BTW.
Not my pic BTW.
What brand alkylate fuel are you running?
thompsoncustom
ArboristSite Guru
I think what is consider rich needs to be defined in this case. almost all saws are gonna be on the rich side even if it's at a very small amount from someone that knows what they are doing tuning by ear. The only way you could be 100% is with a computer setup and I'm not talking about auto tune.
I agree that excessive build up in the muffler is a sign of them running to rich. I think your spark plug looks like it's tuned great and looks just like mine
But my piston is also a 100% clean.
I should also note that I just run pump gas.
I agree that excessive build up in the muffler is a sign of them running to rich. I think your spark plug looks like it's tuned great and looks just like mine
But my piston is also a 100% clean.
I should also note that I just run pump gas.
Your comments on 1/5 scale rc must be from a 1 engine experience. Most 26-35cc engines will sustain 20k rpm all day on a solid tune. Boats and planes run the same engines, only difference is boats have a water jacket for cooling. They still run quite a bit hotter then a normal water cooled engine and specify the same oil as the air cooled versions. Some are air cooled cylinders with the fins machined off and a oitter jacket added. We have rc specific engines running up close to 100cc and still spin way faster then 10k rpm.
In general there is always carbon present in high hour engines.
Most of these guys can tune fairly well and everyone is shooting for max performance. There is also a propensity to run canned fuel for no real reason. even on regular pump gas with a good tune carbon should be minimal with a good wash pattern on the dome of the piston, little no no build up in the ring area or exhaust port.
Not all oils are created equally either, for reason unknown to me many (rc specifically) still run castor oil. It's very dirty by nature and there's no amount of tuning or fancy fuel that will keep it from building up carbon. Other oils to a lesser extent, but oil can and do contribute to carbon buildup.
Tuning, would be the largest contributing factor. Too rich or lean will give different results with rich being the worst imo as far as carbon build up is concerned.
Saw or o. P. E. Specifically it's totally normal to see bad carbon deposits from pore tuning independent of fuel or oil type.
In general there is always carbon present in high hour engines.
Most of these guys can tune fairly well and everyone is shooting for max performance. There is also a propensity to run canned fuel for no real reason. even on regular pump gas with a good tune carbon should be minimal with a good wash pattern on the dome of the piston, little no no build up in the ring area or exhaust port.
Not all oils are created equally either, for reason unknown to me many (rc specifically) still run castor oil. It's very dirty by nature and there's no amount of tuning or fancy fuel that will keep it from building up carbon. Other oils to a lesser extent, but oil can and do contribute to carbon buildup.
Tuning, would be the largest contributing factor. Too rich or lean will give different results with rich being the worst imo as far as carbon build up is concerned.
Saw or o. P. E. Specifically it's totally normal to see bad carbon deposits from pore tuning independent of fuel or oil type.
VP.
Edited: I've also ran a few gallons of Rural King in the saw only.
To be clear I am buying the non mixed four stroke akylate and then mixing my own oil(red armor) with it.
It's hard to tell anything from that plug as it hasn't been run much.I think what is consider rich needs to be defined in this case. almost all saws are gonna be on the rich side even if it's at a very small amount from someone that knows what they are doing tuning by ear. The only way you could be 100% is with a computer setup and I'm not talking about auto tune.
I agree that excessive build up in the muffler is a sign of them running to rich. I think your spark plug looks like it's tuned great and looks just like mine
View attachment 1112316
But my piston is also a 100% clean.
I should also note that I just run pump gas.
I will say again.. that the normal state of a piston, two or four stroke is to have a coating of carbon assuming the engine is tuned close to correctly.
For the guys that think bare metal is right I can only say you haven't been inside many engines.
thompsoncustom
ArboristSite Guru
I don't think anyone is arguing that normally pistons are coated i'm more curious as to why mine is not and I assume it's from the 32:1 but it's all relative I guess as diesel pistons are notoriously carbon coated unless there is water injection involved because then they are steam cleaned all the time.
Also I assume your plug was on a stock compression ratio chainsaw where mine was at 190psi making it burn cleaner.
I do have a ms660 with a expansion pipe on it with probably 50hrs on it since the pipe as been added I should pull the plug and look at the piston on that one as it runs the same fuel but should be carboned up since it forces spent exhaust gases back in each cycle and would be even stranger if it was clean. Also not sure how much heat effects carbon build up but this saw gets pretty warm lets just say when I'm cutting up a log with it and the exhaust warp starts smoking I let her cool down a little.
2 stroke gasoline aero engines, regardless of manufacturer, run slower than cars and boats. Props are much larger. No stock rc gasoline 2 stroke engines run loaded at 20k. Even ported and piped you’re at the very upper limit at 20k. Stock rc cars and boats run loaded 14k-16k
Your piston is bare because it's running rich/cool. The hotter a motor runs the more carbon is laid down. How is the saw ran, what mix and fuel and what's the current max no load rpm? A 32:1 ratio doesn't effect carbon deposition unless your running really crappy oil.
A properly designed pipe does not force exhaust into the cylinder either. A tuned pipe function by first pulling a suction on the cylinder and then by sending a return wave of fresh air/fuel back into the cylinder. If it forced exhaust back into the cylinder this would just dilute your fresh charge, which would be a step backward.
Tom, yes they will and do hit those rpms. Every day, all day. Zenoah, Taylor (formerly rcmax) and ALX. Even the old Cy/dynamite 23-26cc would upper limit 20k rpm out of the box. The only consession I will make, is I had to look up some of the specs for flight amd you're correct there. Seems they really limit the rpm, via some tiny little carbs. Either way, you're wrong with boats and cars.
Sean, can you send me some service manuals that show unmodified / non ported can hit 20k rpm loaded. Better yet a video. Zenoah state 20-22k but that’s all unloaded. Loaded rpm is 14-16. I have never seen a video of them hitting that loaded with a tach unmodified.
Is that like a wiener wash??? 
Regardless of all this model boat engine nonsense, a bare piston is a cool/rich piston. This is basic two stroke knowledge BTW, which you would think one would have a grasp of before making YouTube videos.
Probably due to prop efficiency/safety.
No idea, I got out of flight pretty quick. Costs too much to fix when you crash. I know there's something about maximum tip speeds and some other stuff about what materials the prop is made out of and staying below sonic speeds.
Tom, I'll do you one better. Get in a plane and come over here and I'll let you run any of my 1/5 scale and even take you down to wangner park for a race. There's a great 23-26cc on road stock class. I quite assure you they tach 20k down the straightaway.
Edited: What engine are you running (make and model) that hits 20k? Easier to just look up the specs than get on a flight.
