The picture is a spark plug from a 40cc RCGF twin cylinder engine. The engine is running good, but I decided to pull the plugs to have a look at them. Is it possible to tell from the attached picture if the high speed needle is set too lean or rich? The engine was run at full throttle for about 30 seconds and then shut off right before I pulled the plug.

It looks a touch rich, but if you are happy with how it runs, I wouldn't change anything. Also, 30 seconds isn't really long enough to get a good reading, and the engine should be run at it's normal load, ie, flying. You also need to do what is called a "clean cut", which is running it at full throttle as long as is practical, and then immediately kill the engine without letting it idle at all.

All in all, plug reading is a difficult and somewhat unreliable method of tuning model airplane engines. This is further complicated by todays crappy gas, which gives varying and difficult to determine plug readings.

So, with all this in mind, "If it works, don't "fix" it".

AV8TOR

I have to agree with av8tor, the plug looks good, so what if it is a little on the reach side, that's where we want it anyways, my VVRC's 40 twin plugs look just about the same and I'm happy, very happy with the performance of the engine.

Thanks for the comments guys. I'll leave things well enough alone since the engine is running good.

Greg

There are a million things you can learn from a plug but you have to do like above and run a brand new plug, full power if the plane can do it and then keep the throttle full open and kill the ignition. You will need good eyes or a scope. You can do all this and chase readings around and eventually end up back where you are now. If it sounds good, turns good numbers and reliable then dont mess with it. If you are looking for more power then get a bigger engine.

Not too bad , Spark plug always burn like this because two stroke oil mixed with gas and burned together !