Im sorry, but im pretty new to this game, and would like to know something new. I would like to know how to tune an engine. What is the aim of tuning? What is too lean or too rich? I understand everything else except the engine. Im asking this because i might be the only one on the field one day and i would like to tune my engine myself.


THanks alot guys

Samolot

Rich and lean refer to the fuel/air mixture entering the engine. A "rich" mixture means there is more fuel than optimum for the amount of air. A lean mixture has an excess of air. A lean mixture causes the fuel to burn faster, and consequently hotter. There is an optimum mixture where the engine will run at peak rpm when at full throttle, and this mixture is controlled by the high speed needle valve, with a small contribution from the low speed mixture.

The objective of tuning is to adjust both the high speed and low speed mixtures such that the engine achieves peak performance in the air, does not run too lean and damage the engine at full throttle, and idles reliably at a relatively low rpm (typically 2500-3000 rpm).

Tuning is not magic. It is methodical, and once you understand how to do it, you will be very satisfied.

First, understand where the high speed and low speed mixture adjustments are located. The high speed needle is the larger knob, normally on the left side of the engine, and is close to where the fuel inlet line is. 2-3 turns out from the full in position is a good average starting position for a new engine. Turning the knob out (clockwise) will make the high speed mixture richer (more fuel). Turning it in (counter clockwise) will make the high speed mixture leaner (less fuel).

There are two types of low speed adjustments, depending on your carb type. Most of the higher performance engines have a low speed needle valve, generally as part of the throttle barrel, and is adjusted by a small screw inside the throttle arm. Like the high speed needle, adjustments out (clockwise) add more fuel to the mix (richer). Adjustments in (counter clockwise) provide less fuel (lean). This low speed adjustment controls the mix up to about 3/4 of the throttle, so its very important to be set properly for a reliable idle and good transition to full throttle.

The second type of low speed adjustment is an "air bleed screw". This is readily identifiable by a small hole in the front of the carb with a small screw that opens or closes across the hole. In this case, rather than modifying fuel flow, it is modifying air flow at low speeds. Turning the screw out (counter clockwise) adds more AIR to the mix, thus LEANING the low speed, and turning the screw in (clockwise) reduces the air flow, thus making the mix RICHER.

To tune the engine properly, start from the factory settings. Start the engine, warm it up, and remove the glow igniter. If the engine stalls immediately, its probably too rich. Turn the high speed needle in about 1/4 turn, and try again. Once the engine is running without the glow igniter, go to full throttle, and turn the high speed needle in (clockwise) until the engine reaches peak RPM. Give the engine time to respond as you approach the peak. Use a tachometer. It will make the job much easier. Once you have found the peak RPM, turn the high speed needle back out (counter clockwise), until the RPM is reduced 200-500 RPM below the peak. This ensures a slightly rich mixture at full throttle to prevent damage.

Now its time to check the low speed mixture. Reduce the throttle and adjust your throttle trim setting until the engine reaches its lowest reliable idle speed. This may be between 3000-3500 rpm to begin with. Don't worry. It will improve as the mixture is adjusted. Allow the engine to idle for 15-20 seconds, and then push the throttle open quickly. If the engine hesitates, stumbles, and then goes to max rpm, your low speed idle is slightly rich. Turn off the engine, and lean the low speed mix, BUT NO MORE THAN 1/8-1/4 TURN at a time. After you make this adjustment, restart the engine and recheck the high speed needle. This is important, as the adjustment in the low speed mix will affect the high speed mix. After readjusting the high speed needle as before, do the throttle transition test again. Repeat this process until the engine transitions smoothly from idle to high speed without sputtering, and it reliably idles between 2500-3000 RPM.

If you do the throttle transition test, and the engine stalls immediately, the low end mixture may be too lean. Make the adjustments as above only richening the low speed mixture by 1/8-1/4 turn at a time.

An alternative to the throttle transition test is to pinch the fuel line at low speed. If the engine rpm rises slightly before stalling, the mixture is rich. If it dies immediatley it is lean. If there is no change in RPM, its very close to optimum. I prefer the transition test, as this more closely mimics performance in the air.

If you have to adjust the low speed mix more than 1 turn from the factory defaults, there may be a problem. Check your fuel lines, make sure the needle valves are clear, that the air bleed hole is not clogged, that there are no air leaks, and that your glow plug is good.

Once your engine is tuned properly, you shouldn't need to touch it again, other than to check the high speed needle at the beginning of the day. After running properly, if it begins starting hard, transitioning rough, or won't idle, your glow plug is probably going bad. Change the plug before you make any other adjustments.

Good luck!
Brad

I assume you are talking about two cycle engines so I will approach an answer that way.

Too rich means there is too much fuel for the amount of air. When this happens the engine runs rough and you get a lot of smoke/oil out of the exhaust. You will not hurt an engine if it is running too rich.

Too lean means there is not enough fuel for the amount of air. When this happens the engine runs very well, until it stops. Running too lean can cause the fuel to detonate before it is supposed to, causing a back fire. Also, since the oil is mixed into the fuel, the engine doesn't get enough lubrication. Running too lean will damage your engine.

There are generally 3 adjustments you can make on an engine to tune it.

The first is the idle stop screw. The original idea of this screw is to set the maximum you want the carburetor to close and thus setting the idle. This is almost useless since due to the type of fuel, how broken in the engine is, and weather conditions, your lowest idle can be different day to day. Also if you have the screw set, unless you have some other mechanism to do so, you can not remotely kill the engine. I always set my screw just past the point where the carburetor closes. and use my trim tabs to set the idle. (When the throttle is completely down and the trim tab completely down, the carb is closed and thus kills the engine.)

The second setting and perhaps the most important is the high speed needle. This is the long thumbscrew that is either directly connected to the carb or remotely attached with a short fuel tube running to the carb. This screw sets the maximum amount of fuel the engine gets at full throttle. To set this what is usually recommended is to turn the screw all the way in (clockwise) Be careful not do turn to tightly as you might break the needle. Then turn the screw out two and a half turns. This will usually create a condition that is too rich, but will be lean enough to get the engine to start. Then you can start slowly turning the needle back in until it runs smooth. You want to get the engine to a point that if you pinch the fuel tubing it raises in rpms slightly right before it dies. And that if you hold the model vertical at full throttle it will not die. If it is a brand new engine you want to set the needle about two clicks out (richer) than this setting for at least a gallon or two of fuel.

The last setting is the low speed needle. I have seen this just about anywhere on the carb, you'll have to check your manual to see where yours is. This needle sets the minimum amount of fuel the engine receives at idle. Setting too rich means that idle will be rough and high and transitions will be groggy. Too lean means that the engine will die at idle and transitions will be slow and it might die.

All of this is just general information. For info specific to your engine, check the manufacturer's manual. Since this is your first engine I highly suggest you get someone to help you the first time. These engines are dangerous and if you don't know what you are doing you can get hurt easily. Also the wrong settings can potentially damage your engine.

The basic aim of tuning is to get just the right amount of fuel going into the engine by adjusting the flow through the needle valve. Winding the needle out lets more fuel flow through and makes the mixture richer. Winding the needle in does just the opposite of course.

It's much much safer to run an engine too rich than too lean. Too lean means it'll get very hot and could do serious damage. Too rich really just means lower revs and not as much power. The trick of course is knowing if it's running rich or lean (at full throttle). If you can see a fair bit of smoke coming out the muffler then chances are it's rich. To know for sure just open the needle a little more, slowly, and listen to the revs. If the revs drop then it's rich and you're on the safe side. If the revs rise a little at first and then start to drop then you were a little too lean to begin with.

When you know for certain it's a bit rich then you can lean it out slowly and listen to the revs increasing. You'll get to a point where you start to wonder if there's been any change so stop...no leaner because you've now got peak revs or maximum power. But this isn't good to fly with because the engine will go leaner in flight and overheat so wind the needle out to make it run a bit richer and listen for a distinct drop in revs. If you've got a tacho then aim for about a 500 rev drop from its maximum.

This is only for tuning the high speed mixture and only with an engine that's been run in, not a new engine. The main thing to remember here is that rich is good and lean is bad!

It's probably best not to overwhelm you with information at first, just get you into the basics.

On a throttle equipped R/C engine there are 2 settings to "tune". At wide open throttle you'll adjust the high speed needle valve to get the correct ratio of fuel to air going into the combustion chamber. When you open the needle valve you'll allow more fuel per given unit of air to get burned. The engine will slow down from it's sceaming high pitched peak and start to blubber. Too lean and the engine will keep the high pitched scream but slow and die.

Don't even worry about the 2nd setting - the low speed idle until you are comfortable in adjusting the high speed needle correctly.

Our model engines are cooled by air AND the fuel which contains a certain ratio of oil - 16, 18, 20, 25% or so. You'll never see reputable fuel sold with less than 16% oil so the markings on the container of 5%, 10% and 15% don't pertain to the oil content but to the nitro methane content.

A rich mixture is generally easier on the engine as it allows it to run cooler. The older engines with iron pistons and steel cylinders required a long break in of careful running on a rich mixture. Modern ABC type metalurgy needs to be brought up to operating temperature fairly quickly as they are fitted extra tight when cold. As soon it is started it needs to be adjusted to near it's peak setting, then can be backed off slightly.

Any new engine needs help by... Running a mild fuel with ample oil content; running a slightly smaller propellor to decrease the load on the engine and; running in a rich or nearly rich setting.

Follow the engine manufacturer's instructions. A good engine will run you $100 or better - depending on the size. Learn to "listen" to it and care for it. It will give many years of great service. A poorly treated engine will live a very short life and never develop it's potential.

Harry Higley's yellow book, "All About Engines" found in hobby shops offers great information on model airplane engines.

Some great responses here. I'd like to highlight something Brad mentioned. Once an engine's been tuned (and run a gallon or two of fuel through it), you shouldn't ever have to adjust it, so no worries about flying alone. If the engine starts giving you trouble after it's been tuned and broken in, it's probably not the engine.

A thin trail of smoke in the air is a pretty sight with a new engine (or even not-so-new). That indicates a nice, cool rich mixture.

The only other thing I would add is that the usual tuning methods (as descibed by Brad) work fine on an engine where the low-speed adjustment is somewhere close to where it should be. That's almost always the case when you buy from the manufacturer or distributor. If you buy a used engine, you never know. If the low-speed setting is off the engine will be very reluctant to start, no matter what you do with the high-speed needle. On an air-bleed type carb, a half-covered bleed hole is somewhere close. On an all-needle carb, it's hard to tell. Best advice is, don't mess with the low-speed needle unless you have to, and then make your adjustments 1/8 turn at a time. 1/8 turn makes a big difference.

WOW, great replies everyone, give me an hour to read em all!

Not always true, but generally speaking, yes. Air density will necessitate some fine adjustments occasionally, depending on how stable the weather in your location is. A fine, dry (non-humid) day in the South is relatively rare, but on those occasions the mixture needs to be richened a tad, conversely if you're set for arid weather, and it gets muggy-humid, like August in Charleston, SC, then you might need to lean the mix because the air is less dense then.

This summer here in NC has been like that. June came, was way wet, then it dried out enough that I had no rain, zip, nil, nada, at my house for two months, and the humidity (normally around 60-75% here) dropped into the 35-40% range, and was significant enough to require retuning several clicks of the needle on all my Saitos.

I couldn't disagree more. My personal opinion and that encouraged by my club is that solo flying should be avoided if possible. Yes, we all do it but who is going to drive you to the hospital when you seriously cut yourself with a prop. No worries? WRONG! More worries, a time to pay extreme care as there is nobody to help you.
Our club President was starting his plane one day and foolishly reached across the prop for the glow ignitor. Well, he got his arm in the prop and cut an artery, not a minor injury by any means. Fortunately there were several other members there to help. Fetching clean rags to cover the wound, securing the plane, driving the car to the hospital, etc. Hard to do all this when alone.

Okay, I should've said, no worries ABOUT THE ENGINE if you decide to go flying alone. Sheesh.

Whenever you make an adjustment to your high or low end needle you need to do back up checks to see if what you did had any effect and throttling up does not tell you anything. You can have smooth transition in rpms and still be too rich or too lean.

It makes no difference to me if I'm the only one at the field or I'm surrounded by a hundred people. I have no intentions of losing fingers or slicing arteries so I always take extreme care of the prop the same as I would if I was using any other machinery like a circular saw or band saw. Carpenters lose fingers by being careless, butchers lose fingers by being careless. Always treat the prop as though it was twice as big as it really is. Plan every move you're going to make like removing glow ignitors or reaching for the needle valve, get into a routine and don't rush anything.

Now this is just my opinion but I think electric starters make people more careless around props because they have no real contact with them and tend to be less aware of the dangers. Until they have contact!

Seeing how everyone is on the matter of safety on solo flights being the only one on the field. NO worries is possible for me. TEchnically im never alone on my field, im just alone on my field that knows how to fly. My dad is with me/. HE drives me. HE enjoys to watch me fly. If anything were to happen, im not the only one there. Not yeah, i couldnt agree more with the fact that safety is an importatn issue. Our club enforces the "dont fly alone" rule. I think its great, but they should also mention that you can fly alone as long as you are accompanied by another person, regardless of experience in the hobby,

No matter how careful a person is, accidents can and do happen. Accidents are called that because they are just that, and accident. Otherwise they would be called a "I planned on doing that". To say that an accident will never happen to you because you are safe is just sticking your head in the sand to avoid the real world. I wear my seat belt in my car even though I consider myself a very safe driver. Why? Because accidents do happen. And the same is true with our planes. What happens when you are starting your plane and the prop nut comes loose and spins off and cuts your hand? What happens when the rope you tie your plane down with comes untied? What happens when that 4-stroke motor you are tuning backfires and throws the prop?

My point is that accidents happen to the people, even when they are being safe. A case in point. We have a gentleman at our field who has been flying for almost 20 years and has never had an incident. He is always very safety minded and doesn't ever do anything careless. He secures the plane tightly when starting the plane. He stands up and walks around the plane to remove the glow driver. He stands behind the plane to adjust the needle valve. I could go on, but you get my point. On morning he bend down to adjust his plane when his sunglasses slipped off. His first instinct was to try and grab them as they fell, (yep, you guessed it) his hand was hit by the prop as he reached for his sunglasses and got a good gash in his hand. We cleaned it up as well as we could at the field (using a first aid kit that I keep in my truck) and then we loaded him up and took him to the emergency room. He was bleeding pretty well even though we had his had wrapped up with a towel. Between the bleeding, the pain, and the heat (normal summer day in Oklahoma is always hot) he passed out on the way to the emergency room. Now what you would have happened if he had been alone? What would have happened if he passed out before he could even get in the car??

With all of that in mind I won't fly alone at the field. There are just too many things that could go wrong out there.

That's my 2¢ worth.

Ken

How about the guy that went flying by himself and tripped as he was getting out of the car, hit his head and passed out. He laid there for ???? how long before someone else showed up. It's not a good idea anytime but we all do it sometime. ENJOY !!! RED

I'm going to go against the norm here. Allot of times I have no other choice but to fly alone. Yep, there I said it. I know it's dangerous. I know the risks involved and I have been bitten by a prop on one of my electrics while sitting at home with family around.

The reasons are pretty simple. About 95% of our club members are retired. Almost everyday at 10:00am they get together for breakfast, then head to the field to fly. By the time I get off work, they are all heading home or are already at home. The other 5% that do work are younger than me or close to the same age but have wives/kids that they must attend to. I'm single and both my girls are on their own so I have no worries about needing to be in a certain place at a certain time.

I have spent more than one evening waiting at the field for someone to show up from about 4:30pm to 8:30pm only to end up mowing the grass because no one showed up. Yep, I called people and they were too busy to fly. Sometimes someone does show up late and we have the "normal" evening crowd that are the same people all the time but those days are too few and far between.

I can hear it now, this guy is nuts, he's dangerous and all of that and he's gonna get hurt. I understand that an accident can happen. I expect it will some day. All I can say is it is a risk I prefer to take.

I'm lucky, I have the time to fly and I do compete so I need to practice. I do have a caller but that person works also and in the evening so I'm left with little choice.

I've met Bubba, and I totally understand why people won't fly with him

HAW!

I'm surprised you would even admit to meeting me

Oh and btw...take a look at Minn's review videos, take notice that he is either in the air alone or everyone goes to another spot in the airspace...HHHMMMM

Guess I'm going to have to call your wife and tell her not to let you play with here for a while


HAW HAW

I know the subject has been changed a bit to safety, but I still need some engine help.

My instructor has my engine set rich enough to be blowing a lot of fuel out the muffler. Normal?

Also, I have been flying recently in temps ranging from 28 deg F to 70 deg F in a couple of days. I will have to richen the high speed adjust for colder weather?

From some advice above, I know that I'm already needing to adjust my low speed idle (didn't even know I had one) because of a major hesitation going to full throttle.

Thanks-

Talk to your instructor. He may have it set really rich because its a new engine. If you've got a few tanks of fuel through it (assuming its the typical ABC or ABN engine), then you can lean it out further. Peak the RPM with the high speed needle, then richen up until RPM reduces between 200-500 RPM. Then check your transition. A very rich top end can make you thing the low speed setting to too rich, and can cause similar hesitation on throttle up because you're dumping too rich a mixture into the engine.

I always check the high speed needle at the beginning of the day, and then again after the first flight. If the temperature warms up significantly, its cheap and easy to check it again. Invest in a tachometer. It's well worth it. I normally don't have to touch the low speed mixture once I've got the engine tuned.

Some oil out the muffler is good. You don't want the oil coming out to be "burned" or discolored. That indicates the engine is running close to the breakdown point for the oil. A trail of thin white smoke behind your plane is usually an indicator that things are running properly. Depending on the oil content of the fuel, you may be cleaning a lot or a little oil off the plane at the end of the day.

Brad

Oil coming out the muffler is good. Fuel droplets spitting out is too rich for flying. I agree with Brad that it might be a good idea to ask your instructor, but since he set it there, he obviously thinks it's okay. But it might be useful to hear his philosophy on the subject.

You may well have to lean out the low-speed setting to improve the transition, but the high-end has to be close to optimal (I'd say no more than 500 rpms below peak) before you do that, or else you'll be chasing needle settings all day. Even if you don't think the engine's broken in enough to run near peak rpms all the time, set it there for the few minutes it takes to adjust the low-speed. Afterwards you can richen it out to your own preference. When adjusting the low-speed, lean it out 1/8th turn at a time until the hesitation is gone, or at least almost gone. (You should stop the engine each time you readjust--safety again).

On most of my planes I run a rich mixture all the time and never adjust the needles, but that's just me. I hate fiddling with engines.

By the way, how can i stop the muffler from rubbing the two halves with each other? I always have a dirty wing. I tried tightening it but it only made it worse. I didn't know that two metals rubbing together can do that. My instructor mentioned something about a thread locker. What is that? By the way, some good laughs and good advice in this post. Ill try to tune the engine my self when i get the chance to.

Well, his rationale for running rich is due to the cold weather.

I've got about a half gallon through my Nexstar already. Sounds like I should get a Tach, right? Any suggestions?

What the heck is a tach? Send the link and well check it out. I would think an easy sport is a great one to go form the trainer.

Ok so i got the engine terminology down. Im going to the club this weekend to check out what i have learned. This site is great.

THanks guys,

And if anyone wants to submit anything else, ill read it.