Jetdesign

My Feedback: (8)

For the past year I've been adjusting my idle mixture based on transition from idle as per manufacturers instructions and what I've read on this forum. Irecently had to learn how to work an air bleed adjustment on my YS, and the directions for that were to tune the mixture to maintain a steady idle RPM over a period of 15 to 20 seconds, and not based on transition or a fuel line pinch.

I'm not 100% sure how these carburetors work, but it is my understanding that the engine uses suction from the piston's down stroke to draw in air and fuel at idle; with the carb barrel in the idle position this places a good amount of suctional draw on the spray bar, pulling in fuel. So no matter what style of mixture valve is on the engine, the principle is the same. Please let me know if I"m missing something here.

So, Iapplied the same methods to tuning my 2 stroke engine, by setting high end a few hundred RPM down from peak, then dropping to idle and watching the RPMover 15-20 secons. My transition was totally fine, even after a short period of time, but Istill found that the RPM was dropping after maybe 10 seconds ( i.e. loading up with fuel). Ileaned out the mixture by about the thickness of a small screw driver blade each time and repeated. After 2 small adjustments Iwas able to maintain 2100 RPMidle for quite a long time.

Iwas able to drop my throttle trim and get a really, really good and reliable idle, and had an immaculate transition to full power.

So this worked really well for me. Ifigured it would be a good idea to post it and see if this is what other people are doing, and finding out why they aren't if not. I think it's important for people to understand how these things work and how to care and maintain them properly. Iand others have certainly had tuning issues with things not working out the way we think they should, and we all know how frustrating that can be.

This is such a simple thing to do and adust for and could have saved me a ton of time 'waiting for an engine to break in' or wondering why my midrange was not as crisp as it should be. Hopefully others can learn and put an end to their frustration, too.

redfox435cat

you on the right track. For me doing the pinch and trasition tuning of the low end is a simple way to convey how to get it close, it's also quick and fool proof. I get it close this way in a minute or two

Once it's "close" yea your within a half turn either way on the low end. Then I just basically play with it , nudging the idle a few degrees either side until I'm happy. which takes time, 10-15 min. The hard part for me is figuring out if the engine is broke in or not, and really hard when it's someone elses asking me to help and not knowing the history of the motor.

CGRetired

My Feedback: (1)

This is not quite a beginners topic.  Not many beginners will be dealing with tuning a YS four stroke engine.  Please consider posting these sorts of comments in the proper forum.  Although interesting, it sort of goes way over the head of the beginners trying to figure out what battery pack they should use on their park flyer. or what prop to use on their OS 40 LA.

CGr.

Campgems

GGr, I've got to disagree that this isn't a beginners topic. Tuning an engine shouldn't be one of the last things a beginner learns. I sure know it would have saved me a lot of greif when I was on the buddy box. No, I didn't have a Y.S, but I did have a four stroke.

I don't think that tuning an engine is over the heads of most beginners, and it shouldn't be over the head of any of them..


Don

Steve Steinbring

Joe,

I haven't adjusted a YS bleeder as of yet. However the bleeder carb carbs on 2 cycle glow engines work a bit different than those with a low speed needle to adjust. As you open the bleeder screw you are in effect leaning the mixture or adding more air to the idle mixture setting. Thats because you are controlling the air mixture not the fuel. So if you close down the needle it gets richer less air introduced into the mixture. I also use the pinch test to get the mixture set correctly. If anything I prefer the verge of being a bit too rich which the engine transitions well out of over being a bit too lean.

CGRetired

My Feedback: (1)

Campgems  I wasn't arguing the point, I was just suggesting that it would get more exposure in the engine forums.  If you guys want it here, that's fine. 

CGr

Jetdesign

My Feedback: (8)

I was just trying to get an educational thread about tuning in the beginners forum.

I understand the bleeder valve on my YS is different than the carb on my OS 2 strokes, but the principle is the same - adjusting the mixture of fuel and air at low engine speed. YS engines, despite the pressurized fuel system, do suck fuel at idle speed like a standard 2 or 4 stroke.

The point I was hoping to make - if it is correct - is that tuning any of these engines so that they maintain a constant idle RPM for a period of time seems to be the most accurate and reliable method I have found.

I agree the transition quality and pinching the lines gets you close, but if you don't have tons of experience where do you go from there? I feel like the steady RPM way takes some guessing out of the game.

I wish I had known this a year ago, which is why I'm posting it in the beginners forum.

RegFlyer

Hey!!!!! Iasked that exact question about props..... lol

redfox435cat

are we playing the dificulty police. your kinding right
seriously, enough have posted about low end tuning over the last month that some have gotta be ready to take it to the next level.
I've run into plety of noobs that for some odd reason they end up with 1500 dollar planes and bringin them out wanting us to fly them. Don't know about you but I'll take em up on it. People inherate this stuff all the time.

GaryHarris

Theres an engine forum?

beau0090_99

Hey Joe,
I think you are right, despite the engine, if the thing will not idle at a consistant speed, then it will slow down and die. Kind of like standing on a wet log. If you are not in the center, things aren't going to get better, you will fall off one of the sides. Also, with the idle mixture being tuned well will lead you being able to lower your idle speed and theoretically slow down your approach speeds at the same time.

I have this problem with my floater planes, they idle just a bit too high and their descent rate is way too shallow, makes for a long landing approach.
Curtis

Jetdesign

My Feedback: (8)

Exactly. So set the thrttle to idel and watch RPM. If it speed up, the mixture is too lean. If it slows down, the mixture is too rich.

CGRetired

My Feedback: (1)

Yep. Pick one: http://www.rcuniverse.com/forum/default.asp?forumid=463

doubledee

My Feedback: (4)

Take it easy here. gaRCfield only mentioned the tuning of his YS engine because of what the learned on the air bleed carb. The real point is his tuning tip that applies to all 2-stroke engines.

Very good info and pertinent to beginners learning to tune their engines.

After all, if you're not a beginner, you don't need any advice as you should already know how to tune an engine.
I learned to tune an engine while I was a "beginner".

Keep it up, Joe.

CGRetired

My Feedback: (1)

GaryHarris asked for the engine forum and he got what he wanted... a link to it.  I took that question as apparently he didn't know there is such a forum. 

Just because I was offering to move it to the engine forum where I thought it belongs, doesn't mean I don't appreciate what's posted here.  As I said, not many beginners start out with a YS engine so I thought that perhaps this might have been better off in the engine forum.  I thought I pointed that out in my reply to Campgems.  Consensus noted that they like it here and there is nothing wrong with the thread, so here it stays.

If I thought It in fact belonged over there, I would have moved it.  Don't put something into the posts that are simply not there. 

Go ahead, gaRCfield.. do your thing.

CGr.

goirish

I know some guys that are very good flyers, but, not very good at tuning the engines. I think what might be easy for some, may not be for others. I am always interested in how one tunes their engines. I have learned "mucho" about tuning on this forum.

Lnewqban

gaRCfield:

Could you explain this a little better for me?

Sorry, but I see no difference between what you were doing before and now, other than switching from idle needle to air bleed.

CGRetired:

For some reason, many members are not aware of the engine forums.
May be showing a link within RC Airplanes forums would help?

There are also very interesting forums about full scale airplanes, batteries, radio systems, unusual models and video and photograph here in RCU.

planebuilder66

My Feedback: (8)

Yes the good old airbleed carbs, many beginners will see these, they are on the plain bearing 2 stroke engines very often, on a side note, they are very prone to issues when the tank is too high or low in relation to the carb. But the concept is the same as any low end fuel circuit, except instead of having the air volume fixed and the fuel adjustable, the fuel passage is fixed and the air volume is adjustable. Many are correct in the fact that the pinch test will get you close, but a little more time spent tweaking the idle so it can do so reliably for at least 3 minutes will assure you that it's going to drop to a nice steady idle, yet not flame out due to a lean transition. Main needle has some effect on it in flow to the idle circuit, so if you touch the high needle, just verify the idle is still correct. They are not hard to adjust, just limited in range of adjustment, so you have to pick a good compromise between high and low. To date, the only carb I've tuned that requires alot of patience and testing to get right is a 3 needle carb seen on many high-end italian R/C car engines. Those have a needle for high, low and mid.

CGRetired

My Feedback: (1)

I thought I did post a link to the thread.... in fact, I did. Look above at my post # 12.

CGr.

bkdavy

My Feedback: (1)

My experience with air bleed carbs has been that the principles of tuning are the same, whether air bleed or spray bar adjustable. 

Now as to the concept of adjust it until it maintains a constant RPM at idle for 15-20 seconds.  Using one indicator alone doesn't work well.  I've seen engines that would hold  a very steady low idle forever, but when you checked the transition, they would immediately die.  Thats because an engine that is running lean at the low end (not a damaging condition by the way) will run very well.  It just won't have sufficient fuel left in the system when you punch the throttle for the transition, and it dies.  Use BOTH tests (idle reliability and transition) to determine the final adjustments.  The pinch test is good for rough adjustment, but its harder to judge the small RPM change you get as you get close.. 

And remember, what we need is not the low reliable idle.  What we need is a reliable smooth transition.  We can land a plane deadstick, but if the engine won't spool up when you abort an approach, you're asking for problems.

Brad

tony0707

hi  getting engine idle right is very important-  if the engine does not keep and idle for a long time-it is not right-and it should come off that long idle and screem up to your rich top end setting -then your are very close to perfect-  may need some fine tweekingfor most engines on the low end and top end i use the -squeeze the fuel line method to get into the ballparkbut i do find that depending on the type of glo engine you are using-the idle will vary between almost no rise in idle  RPM -to a 2-300 RPM rise in idle  RPMthat is were the tweeking comes injust run the top end 2-300 RPM max off your max RPM numbers-that will be fine for all glo engines-i do use castor oil in my fuel  80/20 mix-and i do like to get power out of my glo stuff-and cause no damage after 20 years that way

Jetdesign

My Feedback: (8)

Before I was adjusting my low end based on transition from idle to WOT, and by pinching the line and noticing the reaction at idle. I am now setting the throttle to idle with a tachometer and watching the change, if any, in RPM only at idle setting.If you drop to idle and the RPM slowly starts to increase, you mixture is lean. If it decreases, the mixture is rich.There are different styles of carburetors, but they are accomplishing the same thing - adjusting the fuel and air mixture going to the engine. Both are turned to make the adjustment leaner or fatter, regardless of what direction you must turn each individual one.Again, I posted this because the methods explained in the manuals, i.e. basing the judgement off transition and pinching the fuel line is very subjective - what might sound like a good transition to one may sound boggy to another. Using a tach and watching RPM at idle is objective - look at the numbers and see what they say. Of course with time you can learn to hear the difference, but it's so slight that a beginners ear may not hear the engine slowing down.

tony0707

HI   GARCfieldi like your idle set up with a tach a lothave to give that a try-when the engine is set up right there is no mistaking a clean screeming run up to top end  from an idle -with any boogy condition  -if you are bogging you are to richthe pinch the fuel line thing-is just to get you close to were you need to be -but getting it right on the bench is what you want to doyour flight is only as good as your engine runs  !!

Lnewqban

Thanks, gaRCfield, now I see.

Yes, I too try to find the minimum idle rpms, but that not always allows a good transition.

As stated above, there is a compromise between both regimens, for which the flame inside the engine remains burning.

At pure idle, there is an optimum air-fuel mix that allows a stable flame at maximum temperature. A little more of air (lean mix) or fuel mist (rich mix), and the flame will cool down until a flame out happens.

During transition, the mix leans itself because the air is lighter that the fuel, and it is easier for it alone to rush into the vacuum of the crankcase. At the same time, this rushing mix is cool and can also induce a flame out when it reaches the combustion chamber.

Nice low idle is easier to achieve for four-stroke, which are helped by the momentum of the bigger propellers that they are able to swing.

Check this link:
http://www.hooked-on-rc-airplanes.co...ning-tips.html

For my two-stroke engines with air bleed, I tune the idle by opening the air screw and reducing the rpm with the radio trim alternatively. The optimum point is reached just before the engine quits due to excess of air. From that position, I start testing the transition. The trick is to run full throttle before and after each adjustment, and also turn 1/8 or less at a time. Instead of stopping the engine for each adjustment, I use a piece of fuel tube and a stick of balsa to manipulate the bleed screw and stay far from the propeller. The blast of air keeps the stick away from it when my hand is not holding it. Dead sticks are history after I began to do it this way.[sm=thumbs_up.gif]

Gray Beard

My Feedback: (-1)

Joe is setting the low end of his YS correctly. There idle rpm should be set at 2000 but Ihave mine set at the 2000 for flying and when I roll it out to the runway I have my idle switch set for low idle and Ican get mine to just tick over. Ican't remember the rpm right now but it is lower then YS states they should be able to idle. Ihave it set like this so my planes don't get rolled around, 2000 rpm will do that unless you have breaks on the plane.
Once you get the low end set you should never have to tinker with it again, other then BIG weather changes the only time Ifiddel with the high end is if Ichange the prop type or size. Ican't remember except once ever having to reset my low end on my YS engines, set and forget.
Needle tweakers make me crazy to watch, if it ran good the last flight why are you changing it again?? Come winter my high end will need to be opened up 4 clicks and then left there for the rest of the winter.
There is a complete glow engine forum with factory support here on RCU for most major manufactures, this includes YS. If you are having problems it's a good thing to be able to speak with a factory rep.