Doug Kaiser

I started up my first glow engine tonight (Evolution .45). Started right up and ran well. The only thing I noticed is that the engine slightly hesitates when going to quick full throttle. What adjustment do I need to make?

Pylonracr

Lean the low speed needle.

jaka

Hi!
Open the low speed needle!
You have got two different answers, both correct . The question is : How does the engine hesitate? Does it bludder /sputter (low speed too rich) or does it just hesitate without any noise at all (low speed too lean).

HighPlains

My Feedback: (1)

Don't do anything until you have flown it for a gallon of fuel.

Doug Kaiser

It's really more of a pause. If I throttle it up quickly it takes the motor maybe a second to respond and catch up. No sputtering or odd noise.

Doug Kaiser

May just need more time to break in?

impulse09

My Feedback: (3)

Richen the low a bit. If it improves, good. If not, go back to where you were and lean it.

Always tune rich to lean. Lean causes damage, rich doesn't.

BarracudaHockey

My Feedback: (11)

And make very small adjustments at a time, like the width of a screw driver blade, the low end needle on most engines is very sensitive

jaka

Hi!
If it pauses ...the low speed needle is too lean! Open it a some ,like a 1/4 of a turn.
A modern glow engine doesn't need long running in time and should throttle perfectly from the first start, it's only up to the user to dial it in correctly!

ron ward

I agree, break-in has nothing to do with whether the carb is adjusted right. sounds like it's a bit lean.

HighPlains

My Feedback: (1)

Ground idle is not quite as important as throttle response when flying. Since the airplane has forward movement when idling in the air, the engine does not need as much fuel because the load is lighter, so you want it to be slightly on the lean side.

But I would not change anything until you have some break in time in the air on it. Maybe after you fly models for 50+ years your opinion might be different. Check back with me later!

jester_s1

I have to disagree, HighPlains. The engine will turn more RPM at idle when flying, therefore it's pumping more air and will need a richer needle setting.Setting the LSN lean on the ground is a sure way to get deadsticks in the air.

HighPlains

My Feedback: (1)

Disagree all you want. I'm telling you how it really works, idling in the air the engine is unloaded because the prop is not mostly stalled out like it is on the ground. If the engine is turning faster, it also has more suction, thus a larger pressure differential, so you get a higher flow.

JollyPopper

My Feedback: (6)

I love it. Some say it's rich, some say it's lean. How many actually KNOW which way to turn the low speed needle on this particular engine to make the mixture richer?

Doug Kaiser

It would be nice if it was "Lean turn to the Left" and "Rich turn to the Right", but that would be too easy. It's opposite. I've done three different engine test on the ground and think I have it dialed in. It appears the the low speed was too lean.

HighPlains

My Feedback: (1)

It has a low speed needle, so CW leans it. Normal machine screw threads. If it was an air bleed carb, CCW would lean it.

ron ward

it really doesn't mater if anyone Knows which way to turn the needle. the question had nothing to do with which way to turn the needle,....it asked what do I adjust, and what he adjusts is the low speed mixture.

da Rock

Wonder if the low speed needle is too rich or too lean? Want a dead simple trick that works immediately?

It's simple and easy to judge.

After the engine has settled down into idle, pinch the fuel tubing closed and listen. When it runs out the very little fuel left to it, it will either stop or it will speed up and stop. If it speeds up before stopping, the low speed was too rich. Adjust and test again.

Doug Kaiser

I ran the engine through a full gallon of fuel. still having issues. I went back to the hobby store to get more fuel, but they were out of the fuel that I had bought previously so I tried a different fuel. Got home and fueled it up, and all of a sudden the engine is running like a dream. Smooth and no throttle up issues! The old fuel was 15% nitro and 16% oil whereas the new fuel is only 10% nitro and 18% oil (same brand) Is it the fuel or did the engine finally just break in? At this point, I'm just happy that its running right and will just stick with the 10% nitro fuel.

HighPlains

My Feedback: (1)

I generally don't use less than 18% oil in midsize glow engines for aircraft. And I like fuel that uses a blend of 20% caster with the rest synthetic. Not all fuel manufacturers measure the oil and nitro content the same way. The proper and honest method is by volume, but some are giving percentages measured by weight. Since both nitro and oils are heavier and more expensive than methanol you get less of each when done by weight. There is not a signicant difference in nitro between 5 to 15%, but lowering the nitro slightly is the same as richening the engine slightly. Some engine may have slightly higher compression and do poorly with higher nitro fuels, it a bit like the timing on your car, but usually a change in glow plug is all that is required. Sometime it can take adding a shim to the head with some engines. When you start to go to the performance levels of nitro in the 25 to 70% range, things start to get very difficult in engine set-ups, and very few modelers go there anymore. Adding a tuned pipe also complicates engine set-up and tuning. As it is, with the move to electric, there are less people honing their engine skills.

A. J. Clark

I like to leave the idle mixture a little on the rich side. Then if I don't get the engine tuned good on the high end and it ends up to lean in the air I can pull the throttle back to idle. With the idle rich it helps cool the engine and there is less chance of the engine quiteing.

Hydro Junkie

To take this a little further, HighPlains' post is very informative but he missed one little detail that most don't think about. When he said lowering the nitro is like richening the needle, he is 100% correct. The reason for this is that when you add nitro, you remove fuel from the mix. Nitro is an oxidizer, meaning it adds additional oxygen to the combustion process. The effect is like turbocharging a car engine, more oxygen=more power, but at a price. To make use of the additional oxygen, you need more fuel to go with it. Not having enough fuel results in running lean, subjecting the engine to early detonation and higher than optimum heat levels. In your full sized car, this would sound like "knocking". This, just like in a nitro motor, robs power and damages parts. Since I run 50% nitro in my boats, the effect is even more pronounced. I have a marine .67 engine that has a badly pitted head and piston due to detonation, caused by a different issue. Regardless, the general rule of thumb is when you increase nitro, you richen the needles

da Rock

Excellent "insider" information most people aren't exposed to. There is a lot about nitro that isn't common knowledge and seems backward.

Nitro produces less heat than alcohol, which is what it replaces. So the more nitro in the mix the less btu's. So you can make a case for higher nitro fuel burning cooler. And since you usually don't need more oxygen in colder months, the case can be made also that if you're flying in the winter, lower nitro fuel just might run better as it'll put more heat into the engine and the lessened oxygen won't be missed. That of course, should consider what you're actually doing, putting around for fun or racing flat out for blood.

There is also the affect the nitro has on the engine timing. Yup... timing. There are no timing adjustments in our glow engines is there? Well, yes. The fuel mix affects how soon ignition starts in the cycle. And nitro affects that.

Good thing about all this, is almost nobody is running pylon nowadays, or any other "needle critical" glow engines. However, I do notice that running 5% in the winter and 15% in the dead of summer seems to work for my present fleet. In fact, I have a model/engine combination that seemed to be having cooling issues a couple of years back when it was brand new. I noticed I was still running my "winter fuel", the 5% stuff. Switched to the 15% and the sucker ran better. I still made some of the cowling louvers functional (directly behind the cylinder).

Was it the BTUs? or the timing? or the better cooling?

Hydro Junkie

Actually, something some do with boat motors to break them in is to run them on the bench without cooling, other than an oversized aircraft prop, and use the needle to actually regulate the engine's temperature. By running the engine rich, you actually cool the engine. As you continue to break it in, you lean it out a click or two every tank or two until it's close to where you want to run it. At that point, they install it in the boat and head to the pond. One thing to be aware of, however, is that a boat engine has to be set richer to get it to run properly. We run smaller props with a much higher pitch and at a much higher RPM so the load is greater than it would be with a comparable aircraft engine. Just for example, I have an OS 25FP that turns around 17K with a 9X6 prop. In one of my boats, I have a Nova Rossi 21 that turns up to 35K with a 40X56mm prop while in another, it's a CMB 67 running at up to 28K while spinning a 60X90

HighPlains

My Feedback: (1)

Nitromethane is an interesting energy source, but there is a lot of nuance in what it does and why.

It can cool the inside of the engine - somewhat true, since it takes roughly twice as much heat energy to vaporize nitro than methanol. On the other hand it in high percentages can send the piston right out the exhaust in just a few seconds after an engine goes lean. This then requires a new piston, sleeve and head.

Low BTU output - true compared to methanol.

Makes it's own oxygen - somewhat, as it does have oxygen in the molecule. But it still needs oxygen from the air to burn. The big difference is the air/fuel ratio. Methanol needs about 5 to 6 lbs of air for each lb of fuel to completely burn, while nitromethane only need 1.7 lbs of air for each lb. This is known as the stoichiometric ratio, which is about 14.7 for gasoline.

So why does it make so much power? It is mostly due to the amount of mass of heated gases you get on top of the piston that does the work. Since you can run about three times as much fuel through an engine (comparing 65% to 15% nitro fuel), the power goes up considerably. My racing .40's used about 3 oz of fuel a minute on 65%. They also used up a glow plug each flight. And you had to adjust the load and the head clearance based on the density altitude, temperature, and humidity. High pressure days at low altitudes at about 70 degrees and 30% humidity engines ran really strong.