flybyjohn

My Feedback: (2)

To start off, this is an offshoot of another thread I had but wanted to ask a different, general question. The basic question is: If an engine idles great and transitions quickly to mid and full throttle without hesitation, and can sit in any throttle position for unlimited amount of time without loading up or quitting, can it still be too lean at idle to mid throttle and cause the engine to get too hot?

Reason for question: I had a very rich midrange, Idle perfect and full throttle perfect, but midrange too rich (two needle normal carb). I cut the low speed needle taper angle to a shallower angle to allow the needle to remain active for more of the throttle motion. This leaned out the rich midrange and the throttle was very responsive, no hesitation, no loading up and would run forever at any throttle position. I had the high end set at 500 rpm below peak, and got considerable vapor mist out of exhaust at full throttle. My concern was that at idle and midrange, there did not seem to be any vapor coming out at all, which lead to my question if it could be too lean. It runs and transitions great however and I would assume if it was too lean it would just die from lack of fuel.

I don't want to over heat the engine, however this engine is very finicky about a rich midrange and will snuff out the glow plug if too rich. Although this is a general question that could be asked about any engine, the actual engine in question is a Magnum 52 xls blue head. They have been known for a touchy low speed needle and a rich midrange.

Sport_Pilot

If you have a perfict heat on the glow plug the mixture is actually leaner and you don't get much smoke, and very little at midrange to idle. Sometimes you can adjust midrange mixture by raising or lowering the tank a bit, but not by much and it won't work for some carbs. But if you have a clean transition and it is not detonating, I would not worry about how hot our engines are. If you were to run it on the correct mixture of gas it would run even hotter with no running problems, so they tolerate the heat very well. Just as long as you have good oil of at least 20% that is.

flybyjohn

My Feedback: (2)

I have magnum fuel 15% nitro that is only 18% synthetic/caster blend, so maybe I should put a little more castor in my fuel.

jaka

Hi!
You don't set a glow engine by djudging what the exhaust vapor trail looks like, this seems to be a missunderstanding many newcomers! You set an engine by ear! And you set it slightly rich! Any vapor trail or not is not important ,though, there will be considerably more fuel vapor coming out of the exhasut from engine set rich than from an engine set lean...
Setting engines by ear is how racers set there engines and how experienced sportfliers set their engines.

blw

My Feedback: (3)

Jan- while you are technically correct you are still wrong in a way. You can tell when a Saito is too rich by the smoke as Saitos are know to not smoke much when set just right. The reverse is true with most OS 4 strokes. This doesn't tell you what is set right, but it does tell you when you are too rich or too lean depending on engine brand.

I like to use a tach when setting the high speed needle valve. What everyone leaves out of the tuning process advice is the plane isn't finished with tuning until you fly it around and listen to the engine. If it has a smooth transition, doesn't bog down or stumble after setting it 300 rpm rich from peak then it's tuned.

flybyjohn

My Feedback: (2)

JAKA, I set the needles by a tach and the pinch test. Although some very experienced tuners might be able to tell 300 rpm from 400 rpm, I am not one of them. I can find the peak and then back off a few clicks but without a tach, I don't really know how many rpms I backed off, just that I backed it off and it is a little richer. So that is why I use a tach because maybe 300 rpm rich of peak is still a little lean in the air but 400 rpm off peak is just right in the air. When I am at idle or midrange, I use the pinch test. I like to get a little rpm increase before the engine starts to die. The tach comes in handy here too if the needle is set close to peak at that throttle range, because sometimes for me it is hard to hear the quick rpm increase before it dies. In the case of this engine, the pinch test at midrange didn't allow for much if any rpm increase, and the fact that there was no oil vapor out of the exhaust made me question if midrange was too lean. Like I said previously, the engine transitions from idle to full throttle without hesitation but seams to be right on the edge of being lean.

I don't use the oil vapor to tune the engine, just as an indicator as to the state of the engine. I know that with a vapor trail, most of the time it is rich enough. For most engines, you can run on the rich side all day but one run on the lean side might ruin the engine.

I flew the plane the other day and noticed that after a 6 minute flight of good throttle transitioning, I landed, taxied back to the end of the runway and proceeded another take off. When I went to full throttle, the engine cut out, (not blubber, just almost died) and then raced to full throttle. I aborted the take off and taxied back to where I was standing. I held the tail and tried it agian and there was no hesitation, so I attempeted another take off and the hesitaion happened again. I took off and came around for another landing and held the tail again and there was no hesitation. Upon running down the runway again I got the hesitation. This did not happen with a full tank of fuel. I think it might be a little too lean at midrange. My thoughts are that the fuel rushing to the back of the tank causes a momentary lean condition and the engine in mid throttle is already on the edge of lean, so as the engine throttle is pushed to full throttle, the engine goes lean but as soon as the throttle hits full throttle, the engine then is set rich enough to pick up rpms and resume running.

1QwkSport2.5r

Cutting out on throttle transition usually indicates a lean low speed setting. If there is a midrange adjustment then it's a piece of cake. If not, then you have to battle with having the proper midrange mixture while not being too rich at idle. The idle speed may need to be a tad higher to help combat this issue as well as a hotter glow plug.