After taking the weekend to rebuild my plane after my first crash I finally got to the point where I am testing my engine, but it seems to be running to lean or something, but Im not sure how to fix it. Once the engine is started and idles for a few minutes it putters and doesn't sound smooth and if I quickly go to full throttle the engine seems to rev high for a sec or two and then die down to half power and cut off. What is the proper way to tune the engine so it doesn't cut out after an increase or decrease on the throttle? What is the proper way to use the little knob on the side or the engine?

I found this in another forum. Can anyone add to this?

There's one thing to remember about tuning. Rich is good and lean is BAD!
So, how can you tell if it's rich or lean? First, start the engine and go to full throttle with the main (big, high speed) needle turned out 2 or 3 turns from closed. The chances are it'll probably be a bit rich (safe) at this setting so now you have to be sure. While it's at full throttle, slowly open (richen) the main needle and listen to the sound. If you can hear the engine losing revs then it's already rich and getting richer. This is good. If you go rich enough it'll blow lots of smoke and start to sound a bit rougher, more of a growl than a high pitched sound from the exhaust. No problem, that's what's called 4 stroking and you don't need to go any richer than that but it's good to be able to recognise that sound.

OTOH, if after you've started the engine and you begin opening the needle and it starts to pick up some revs before slowing down then you've started off too lean (BAD!) so just keep opening the needle until you hear it sound growly and rough.

Now start winding the main needle in very slowly and keep listening to the sound. You'll hear a point as the revs go up where it makes that growly sound then suddenly goes all high pitch then usually back to that growly sound. Most engines will keep switching between these two sounds if you leave the needle alone and that's called the 4-2 break, meaning it's going from 4 stroke running into a normal 2 stroke then back to 4 stroke. That's about the setting you need to run in a new ABC engine but your 50SX has a ring so it needs to be run in while 4 stroking (really rich).

At this point you know the engine is rich and quite safe to run all day long but for more power you have to lean it (turn in the main needle) even more. Do this slowly and listen carefully to the sound as the pitch from the exhaust gets higher and higher. When you reach a point where you're not sure if the revs went higher then stop and wind out (richen) that main needle until you can definitely hear the revs drop. Don't worry about how many clicks you turn it, just make sure you've heard the revs drop. Then give it a bit more for luck until you're really confident about the tuning.

It all sounds a bit complicated but it won't take long before you're doing all of that in a few seconds.

Did I mention that rich is good and lean is BAD?

If you are rebuilding after a crash, I would check all my fuel lines to make sure that you are not sucking any air bubbles into the engine. Air in the line will make your engine do just what yours is doing. Good Luck, Dave

Hi,

Like David said check all the lines and the clunk in the tank. Often after a prang, (heavy landing) the clunk can get stuck at the front of the tank.

Cheers,

Colin

The advice above isn't good at all. Rich is bad and lean is worse. Right is good. Did you not learn engine tuning before flying your plane for the first time? The best way to learn tuning is to have someone show it to you, preferably an experienced flyer from your club. A distant second is to use the search button and read the myriad of posts on the topic. I will tell you that the needle valve settings should be fairly simple to get right and the changes they make predictable and repeatable. If the engine is erratic, you have a fuel supply problem or an air leak to fix first.

Firstly, I wrote the above for a guy with a ringed engine that wanted to understand what rich or lean running meant. Second, rich running is never bad even with an ABC type engine as I showed in [link=http://www.rcuniverse.com/forum/m_2875125/mpage_1/key_/tm.htm]this[/link] thread.

Follow the advice on checking the fuel system. Be aware tiny breaks or cuts usually near the tubing ends are HARD to see. LOOK CLOSELY! listen to see if the clunk rattles as it should.
A sharp thrust of the plane rearward will often get it right. Be sure the tank is not foaming.
Foam on the outside to isolate vibration is the key to preventing foaming on the inside.
Try this old article. I printed it out and carry a copy or two in my field box.

http://www.smrcc.net/Tips/Engine/2-stroke_engine.html

Rich is bad? Rich is never bad. It's never bad to run an engine on the rich side.. that means it's getting lots of lubrication.

Now I would not suggest that he fly it that way, but it isn't bad. He should understand how to know when it's to rich or when it's to lean.. now lean is definitely not good, engines burn up that way.

The best thing for the OP to do is to carefully read what Downunder put in the linked post, then work with someone that KNOWS how to tune the engine properly, watch closely, and learn from that.

CGr

I didn't mean that rich would hurt the engine, so correct, it's not "bad" for it. But it is bad for flying and will make for a poorly running engine. If there aren't any air leaks and the fuel delivery is good, then there's no reason not to run a properly tuned engine for best power and throttle response. I see guys at the flying field regularly running their engines too rich, either because they don't want to bother with them or because someone told them that always running rich is better.

downunder- no offense intended. You post likely was spot on for the thread it came from but for a new flyer learning to tune it would lead to problems. The best treatment of an RC engine is to be tuned with the mix just right, which the general consensus says is about 300 rpm rich on the test stand or max power with the nose pointed up. There's no reason a flyer needs to tune any other way once break in is done.

No problem, none taken because I misunderstood what you meant by bad and there are so many stories around saying that running rich will damage an engine (ABC type anyway). I fully agree that being shown how to tune an engine is worth more than any amount of words.

But to try to help out the OP, it seems that the engine is running a bit rich at idle (puttering and not sounding smooth) but too lean at full throttle (revs a bit then dies). The "little knob on the side of the engine" I can only assume you mean the high speed needle valve which controls the mixture at full throttle. Wind it out a turn and try going slowly to full throttle again. If it still just dies then open it some more. Most engines will run on the rich side at 2-3 turns open.