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ENGINE TUNING

 Engine break in procedure

For break in purposes use quality mineral based oil at 25:1 ratio. Synthetic oil’s may be used but the break in procedure will be much longer due to the reduced friction properties of the oil. The error factor to cause damage to an engine greatly increases with leaner fuel/oil ratios. Run at least two liters through the engine before switching to a quality synthetic oil mixed to the ratio recommended by the oil manufacture for its intended use.The safest oil ratio is the one that is specified by nearly all 2-stroke engine manufactures 25:1. It ia a misconception to believe you are doing your engine a favour & improving performance by running a lean fuel to oil ratio.

For the standard RC style engines Komatsu Zenoah has no official break-in procedure. They suggest breaking in the engine may be beneficial. The cylinders have a chrome liner treatment with no machine hone pattern for the ring to wear or seat to.


My opinion is to definitely break an engine in with at least 2L of fuel using mineral oil then switching to synthetic oil. Lately I have been bench breaking in engines with a simulated load before mounting into the heli.
Run the engine for periods of up to 10 minutes at a time under moderate load. During break-in time never go full throttle or overload the engine. Allow the motor to idle for a few minutes before shutting it down, this will help to cool it down. Allow the engine to be cool to touch before starting it again. This heating and cooling cycle allows all the engine parts to properly seat themselves to one another. The idea is to add a very small amount of increased load to the motor with every flight, bearing in mind that it is very important to keep the initial RPM low for the first few tanks.

The CY engines have had problems in the past with flaking-failure of the cylinder chrome treatment. This will cause pressure leakage within the cylinder causing engine compression failure & the engine will not start or run under power.
My understanding is that CY have now rectified this problem.

Needle Settings


Needle settings will be determined by geographical location, atmospheric conditions, engine displacement & carburetor model. Make sure your engine has warmed up & that the  choke is fully opened (off)  before you tune your engine. It should also have been allowed to be broken in by running 2L of fuel with mineral based oil.



Initial Needle setting for the Walbero carburettors
;





WT 668 standard on the G230-240RC & G260-270RC. Comes with internal choke. Initial needle settings 1 1/4 (L), 1 3/8 (H).












WT 813 comes with waterfall jet & no choke. Similar to the WT 990, suited to high end speed such as marine rather than Heli use. Initial needle settings 1 (L), 1 1/2 (H).








 





WT 990 standard on the G290RC. No choke or waterfall jet (accelorator pump). Initial needle settings 1 1/8 (L), 1 3/8 (H).





Closing the needles (jets) will produce a higher idle & leaner engine condition, whilst opening the jet will produce a lower idle & richer engine condition to far open & engine will flood then eventually die.
 


For the  WT 990 & WT 813 cards on the bigger bore engines (G290RC) start with Low needle at 1 1/8 turns (L) out & High needle at 1 1 3/8 turns out (H). These carbs are tricky to get right, a tip is to tune low needle first for the first 1/3 of the throttle range (untill the heli is smooth with no four cycling), then lean out the hight screw setting (testing under load) & never go past the low needle setting. One rookie mistake I have made during a rebuild was was to install a WT 813 thinking it was a WT 990 & head scatch why the needle settings where out & running differently. A few other things to watch out for is to aviod the purchase of insulator blocks with only one teflon gasket. Both sides of the insulator block needs to be heat insulated otherwise fuel will vaporize at a higher rate than required by needle settings causing undesirable throttle issues. Secondly clean your carb filter after breaking in your engine ritch, oil within the fuel can block flow of air.

Oils & oil fuel ratio's affect tune. Viscosity of the chainsaw brushcutter type 2 stroke oil has a built in factor of safety & is the best for Heli use. Use this oil type with a ratio of 30:1 or max 35:1 for longevity & risk reduction. Your engine will be in the safe zone even with extreme weather changes . Balancing a tune to within a blades edge with lean fuel oil ratios & racing cart oils is tempting fate & will constantly need to be monitered with weather changes.

If your engine is worked consult your manual or engine blueprint shop as ported engines require more fuel & different needle settings than stock engines. 
Being slightly too rich will not damage the engine, being too lean can cause engine damage especially on lower fuel to oil ratios.

The Stock G290RC can be used sucessfully with helicopters if

1) The air frame has been adequatly designed for use such as the Morphis Kit. When the G290C was first tested in The Maverick, it worked but was a little to viby. The main reason was the Maverick has a very minimal footprint, thinner frames & more cut outs within the frames, this in effect has direct influence on absorption/travel of frequency through the air frame.

2) correct tunning-this engine needs to be in the sweet spot & not to ritch or to lean for that matter.
 

Adjust needle settings once the engine has been
broken in & allowed to run at least a tank of synthetic fuel mix through the system.

Engine tuning must be under normal operational load & temperature.

Low load needle (L) controls fuel flow up to idle loads or approximatly 1/3 of the throttle range & the high needle (H) controls fuel flow for the remainder 2/3 of the throttle range.

One needle setting will slightly effect the other so it is basically a balancing act & if you don't get it straight away just adjust low needle for idle or 1/3 throttle range, once set then adjust the high needle for the remainder of the range.

You are aiming for a constant clean engine sound at hover & climb out (full throttle load). If you play & hold a note on a musical instrument say ‘C’ & then that note changes to B flat then to C sharp, your ear will hear the difference & detect that this is not holding tune (referred to as 4 cycling & a sign of being too rich). So to when tuning these engines & that is what I mean by a constant clean engine sound for both stages of the low & high needle settings.

An occasional burp or splatter means I'm running on the rich side. This will not damage the engine, but if you're to lean & running a very low fuel to oil ratio you increase your chances of scoring a piston & cylinder. I have had emails of guys being advised on fuel ratios as lean as 60:1, its a free world & economy. My opinion is if you are relatively new to gassers use your fuel to oil ratio as an engine fail safe & stay around the 30:1, 35:1 ratio with synthetic oils.

When tuning & making changes to the needles make sure it is in small 1/16 inciments at a time.

I like to say that with Heli's there are 3 stages of tuning or adjustments to be made & m
ost of your tuning will be with the high (H) needle.

1) At 1/3 throttle stick you want to tune your (L) neddle f
or a clean engine note with no 4 cycling or massive tail shakes. You may need to adjust gyro gain if the engine note is clean but the tail wags persistently. In most cases your heli should still be on the ground. If your engine cuts out when idling it is usually a sign of being to ritch.
If the engine is gurgling & bogging down with loss of RPM it is also a sign of being to ritch.
If the engine is popping or raspy at 1/3 stick, then the (L) jet is too far closed (lean) also known as drying out.


2) Now at hover you want to tune your (H) neddle for a clean engine note with no 4 cycling. If the engine note becomes raspy or starts popping you are too lean. If the engine is gurgling you are too ritch. The tail is another good indicator of engine state, the sweet spot will have the smoothest tail authority and clean engine note.
 

3) Now test under a heavy loading by progressing into a full throttle climbout.
When you progress into a climb out, then pull throttle back to hover position there should not be a change in the engine note. If the engine is gurgling & bogging down with loss of power during the climb out the high (H) needle is basically to rich & not reaching full RPM.  A noticeable tail wag when you pull out of the climb out is another indicator that the high jet is rich or too far open.
If your engine is popping or raspy when transitioning from hover to climb out, the high jet is too far closed (lean) also known as drying out. There is also a noticable power ceiling with no increase in power for the last little bit of throttle.

The ideal high jet position is when the heli wants to keep going with noticable power & a clean engine note during the climb out.


When the engine sounds good & performs well you are in the sweet spot & this will be different from everyone else because neddle settings are dependent upon many conditions such as weight, altitude, temperature,humidity, oil type & oil to fuel ratio.

Another important factor to mention is that engine breaking in is usally performed with limiting the engine to low heed speed or rpm (1500-1650), when tunning the engine you whant the head speed to be at around 1850 headspeed range, putting the high needle/engine under a fuller load range. The waterfall jet (WT 813) requires higher rpm/headspeed for a smoother running engine. You will also being to notice that the heedspeed range has an effect on the overall tune &  performance. To low a heed speed & your are riding on the engine rough spot inducing vibration (bogging being ritch), to high a headspeed & you are also into engine vibrations without much power gain (approaching the engine rpm limits & high wear & tear zone). Headspeed is limited by the governor or radio throttle curves. These need to be adjusted when trying to find the optimal tune.

Tuning issues

 2 stroke trouble shooting engine wont start hard to start or hard to tune.

  • Check spark plug is not clogged, clean or replace & readjust gap.
  • Check for adequate spark.
  • Check exhaust is not clogged or blocked with oil & carbon.
  • Check piston for scoring through exhaust port.
  • Check air filter is not clogged or blocked & is clean & dry.
  • Check fuel is circulating the system with the prime bulb.
  • Check that tank is clean & free of debris.
  • Check fuel filters for blockages.
  • Check fuel lines for cracks.
  • Check all carburetor bolts are tight.
  • Check carburetor insulator for warping or replace.
  • Check that billet carburetor insulators are installed with teflon gaskets.

If the vent line is blocked from the atmosphere it will cause the air/fuel ratio to constantly change.

A cracked pickup line will also cause mixture changes.

Engine cuts out & restarts

The Walbro carb has an integral fuel pump which is driven by pressure pulses from the engine crank case. Any leak that reduces this pressure will cause the carb to momentarily cut out and possibly restart. Check the carb spacer including sealing gaskets & condition. Make sure the pressure pulse hole is not blocked or partially blocked by gasket or contamination. A gasket leak in the crankcase itself will also cause this issue.

High throttle at idle & hard to tune carb


If an engine is idling too fast and refuses to come down to a normal idle speed air is getting in past the throttle body somewhere.The most common source is a
n air leak from the carb spacer caused by warping /cracking of the carb spacer or poor gasket sealing. This is a lean engine condition with potential to cause engine damage.  Over tightening of the carb spacer bolts will easily crack this spacer or damage gaskets causing this condition so to will a crash. There has been different materials used over the years for these carb spacers & accounts  why some never have an issue & others night mares. If using an aluminium carb spacer be sure to use Teflon gaskets as they provide the heat insulation for the carb to properly operate.


Engine won’t start fuel & spark systems good


If the piston is scored, the cylinder chrome is most likely also scored, causing pressure leaks of the internal combustion pressure. Check condition of piston from exhaust as this side is more prone to damage than the inlet.
A blocked exhaust, worn piston ring & leaking gaskets will also share these symptoms.


Depending on the gear ratio if the engine is fitted with the WT 603 or WT 668 carburetor & properly tuned & broken in, you may experience a lack of power or sputter as you decelerate in descent (in normal flight mode with lower headspeeds). The engine won’t feel so smooth until you throttle back up again. This usually happens on lower gear ratios & not as noticeable on higher gear ratios where you are hovering more on the high needle setting. The only cure I know of is to change the carburetor or stay in idle 1 or 2.
You may experience this on the Maverick using standard G230RC (on 600 blades) , the same setup on the GFZ & Brute is not affected. Its not a big deal normally in my opinion & you just compensate your throttle management.

Adjusting for various weather conditions


Most of us have noticed the change in any engines performance with a cold winter morning start.
A change in weather conditions may prevent an engine from running at peak performance or may put it at risk to damage especially when running very low fuel to oil ratio’s. For maximum engine performance you need to compensate for the amount of oxygen available in the air due to the following atmospheric conditions;

Temperature

Hot weather requires a leaner mixture setting & cold weather requires a richer setting. Cold air is denser than hot air. The denser, colder air packs more oxygen into the engine requiring an increase of fuel to balance the combustion ratio.

Humidity

Humidity is the amount of moisture (water vapour) in the air. Moisture in the air takes up volume that would otherwise be occupied by fuel-burning oxygen (water molecules are relatively light compared to Nitrogen and Oxygen). Less oxygen means less fuel is required to maintain a proper combustion ratio.  High humidity requires a leaner mixture setting than dry conditions.  The true amount of water vapour in the air varies with temperature, even if the relative humidity percentages stay constant.


Barometric pressure.

 Absolute atmospheric pressure (also known as station barometric pressure) has a great influence on engine performance. Barometric pressure is highest at sea level and decreases with altitude. It is the force exerted on a surface by the weight of air above that surface in the earths atmosphere. A reduction in atmospheric pressure requires leaning the fuel mixture. Weather systems also have an effect and pressure can change very quickly during the day, particularly as a storm front approaches.

Altitude.

Altitude is an important factor that affects the engine’s performance. Air is thinner at higher altitudes, which means there’s less fuel-burning oxygen than at sea level.    Less air (oxygen) means less fuel to maintain the proper combustion ratio. So, running at higher altitudes requires a leaner mixture setting than running at sea level. The general formula for power loss with increases in altitude is 3 percent for every 1,000 feet (350m) above sea level.

In Brief compensating for varying factors:

Higher air temperature: Leaner
Lower air temperature: Richer
Higher humidity: Leaner
Lower humidity: Richer
Higher barometric pressure: Richer
Lower barometric pressure: Leaner
Higher altitude: Leaner
 

Storage 

My practice is to run the carburettor dry of fuel after the day (unplug the pickup line from the tank to shut down). If you are not going to run the heli for a while due to repairs, weather etc, fuel sitting in the carb can turn bad & varnish, causing blockages & if left to long damage due to corrosion. I have been a victim of its destructive properties with a motorcycle project which lay dorment for a few years. I have lately started to use sta-bil which is a fuel stabilizing additive which will not allow varnishing. But my main recommendation is to run the carb dry after use.

 



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