Beginner Engine Tuning

Beginner Engine Tuning Notes
last updated 11-25-2004

The proper technique to set the engine requires you to do 200-300 ft climbouts... So what do you do if you are a new pilot and can't do that yet, the best choice would be to get help from an experienced pilot. This is because the problem might not just be an adjustment. It could be something like a bad seal in the carb, clunk line too soft and squeezing together, etc. In these cases a more experienced pilot could figure this out quickly and save you a lot of time and frustration. But if you don't have anyone within a reasonable traveling distance then use the procedures on this page. I will try my best to help you get the engine running right.

1. Information related to tuning
2. Tuning tips
3. How to tune the engine (beginer technique)

Information related to tuning

What can make the engine change? This can happen due to the engine breaking-in, from weather conditions, or something failing on the engine. The first two are nothing to worry about, for the last one I'll try to cover some things to look for from a new pilot perspective.

Definitions:
Too rich: no this doesn't mean you have too much money, I wish it did :) but what it means is the engine has more fuel then it can burn. For the engine to run it's best it needs to have the correct amount of fuel to mix with the air inside the engine. Most engines have two needles, a low speed needle and a high speed needle. The low speed needle effects the range of operation from idle to hover. The high speed needle effects the whole range when you adjust it, but it's main purpose is to effect the top third of the throttle. When the engine is too rich, whether it's the low speed needle or the high speed needle, you turn it clockwise to get it leaner.
Effects of being too rich: You will notice that the throttle stick needs to be above the normal hover position to keep the helicopter in a hover. Also you may notice the tail kicking.

Too lean: Lean is not a good condition. Running an engine too long this way can damage it. Lean means that there is not enough fuel/oil mixed in with the air. To richen it you need to turn the needle counter-clockwise.
Effects of too lean: You will notice that the throttle stick needs to be below the normal hover position to keep the helicopter in a hover. And when you land the helicopter the engine takes more then a few seconds to settle to an idle speed. Also if lean long enough then the helicopter will lose power and you have to start raising the throttle to keep the helicopter in the air.

High speed needle
Clockwise leans it, counter-clockwise richens it.
Adjustment sensitivity is high. Most adjustments only require 1 or 2 clicks. If off a lot then 4 clicks.
Effects: total range, but it's main purpose is to effect the top third of the throttle. This needle effects the TOTAL fuel flow into the engine. This means that when you lean it, you are also leaning the low speed setting (the part from idle to hover). And when you richen it, you are also richening the low speed.

On standard two needle carbs the high speed needle is the one with the thumb screw type needle as in the picture to the left. Some engines have two thumb screw needles and the high speed needle will be the one located at the place the fuel line connects to the carburetor. The other will be the hover needle.

The low speed needle is inside the throttle arm barrel on most engines. It uses a flat blade screwdriver to adjust it. Clockwise leans it, counter-clockwise richens it. The adjustment sensitivity is low on the first type, 1/4 turn is a normal amount when making adjustments. If off a lot 1/2 is a normal amount.
Effects: idle to hover range.

On some engines like the OS 50 SX-H and the OS 60 LX-H, the low speed will be on the same side as the high speed needle. Adjustment sensitivity on this type is high. The total range is less then half a turn. Normal adjustments will be just enough to see it move a little. Big adjustments would be an 1/8 turn.

Good info to know:
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It helps to understand what the carburetors job is. What's really going on when you turn those needles??? The ultimate goal of the carb is to provide the right mixture of fuel to air. The air is a mixture of gases but the one the engine needs is the oxygen atoms. You can't control the amount of usable oxygen atoms per volume of air, but you can adjust the amount of fuel so you can get the right ratio. The fuel is mixed with the oxygen so that it can burn when compressed by the piston and ignited by the glow plug. When you 'lean' the engine what you are doing is decreasing the amount of fuel that gets mixed with the air. When you 'richen' the engine you are increasing the amount of fuel that gets mixed with the air. When you adjust the high or low speed needles of the engine you are trying to obtain the right ratio of fuel versus oxygen. Not enough fuel versus oxygen and your engine will be too lean and overheat. Too much fuel versus oxygen and the engine will be too rich and not generate enough power.

	Here you see a typical carburetor. The high speed needle is the one you can adjust with your fingers. The low speed needle is located inside the throttle arm on the opposite side. Some carburators have the low speed needle on the same as the high speed needle. It will have a flat blade slot on the head of it.
	This picture is with the carburetor housing removed. You can see the high speed and low speed needles are colored in red. The fuel comes in through the nozzle in the picture above and into the chamber between the two o-rings. The fuel then goes into the two holes to the chamber where the high speed needle is. The more the high speed needle is screwed in, the less fuel can come in. This would be leaning the mixture. On the right you can see the carburetor barrel with the low speed needle inside. As the throttle servo rotates the barrel it does two things. It lets more of the big air hole of the barrel open up to the ventura of the carburetor case... that's the big hole on the carburetor where you could put an air filter on. Also as the barrel rotates it moves the low speed needle in/out of the nozzle on the left.
	In this picture you see the engine is at an idle. The barrel is rotated clockwise so a minimal amount of air is coming in and at the same time the low speed needle is pushed so far in the nozzle that only a minimal amount of fuel can come out. The fuel and air mix just outside the nozzle and is sucked down into the intake hole of the crankcase.
	In this picture you see the engine is at full throttle. The low speed needle is out of the nozzle, the air intake is fully open, and the mixture at this stage is completely controlled by the main needle. By doing a full throttle climbout you can adjust the high speed needle for a constant rpm.
In these last two pictures you should notice two things. First is that the position of the high speed needle controls the total fuel flow for both high and low throttle. And secondly you should see that the low speed needle effects the mixture from idle up to around 70% throttle.

Tuning Tips:

When you come across an adjustment that you're not sure whether it needs to be more rich or to be leaned then always richen it. It's always better to start out rich. Anytime I am helping someone with their engine and it seems to be off a lot then I reset the needles to a very rich condition because it's easier to start with a cool engine and lean it to get it up to temperature then it is to start with a hot engine and try to get it cooled down. If you do then any adjustments you made will more then likely not be right for the next flight when the engine starts off cool.

Not sure how much to open the low speed needle... Close the throttle and turn the low speed needle all the way clockwise. Open the throttle 20% (idle position). Connect a clean fuel line to the carburetor and blow through it while turning the low speed needle counter-clockwise. When you feel air flow through then you are at a good starting position.

How to Unflood the Engine - read this.

How to clear a hydro-lock condition <Here>

If the helicopter was previously running good and now you see it takes more then a few clicks of the main needle to adjust it then something is wrong. Do not continue adjusting. First change the glow plug. Often times this is the problem. If not then check the line inside the main tank.

If when you start hovering everything is ok then later in the flight you notice to maintain hover you have to raise the throttle up above center (like 3/4 or full stick) then you are too lean. What happened is the engine got too hot and lost power.

A crude but effective technique is to use the position of your throttle stick to determine if you are too lean or rich. Basically if everything was running good, but now on your first lift off you notice to hover your throttle stick is above the middle (like at 3/4 stick or more) then you are too rich. However if at anytime during the flight you notice to hover that your stick has to be below middle then you are too lean, you need to make the engine more rich.

Easy Tuning Procedure

This is for those making their first hover and don't have an experienced pilot nearby that can help. For this to work you need to have the pitch range at 0 degrees for bottom stick, 5 degrees at center stick, and 9 degrees at the top. And the throttle needs to be 50% at center stick and 100% at full throttle (unless this is an OS 50SX-H in which set it to 80%, not the hyper version).

First set the high speed needle very rich. This should be so rich that at full stick it barely will hover. Now take note if the engine transition from idle to full throttle was linear. You should hear a steady increase in engine speed as you go from idle to full throttle. If for example the engine speed steadily increases until it reaches the 2/3 spot then it decreases then that means the low speed needle needs to be richened. The other example is if the speed is sluggish up until 2/3 and then picks up speed. In this case the low speed would need to be leaned.
Once the low speed needle is set for a linear mixture from low to high then you can start leaning the main needle. Lean it a click at a time until you see that at hover the throttle stick is in the center (for a 1/2 stick hover setup).