[hifly2104]

I have a 46 fx by OS that came with a trade last year. Engine is a screamer but will not idle. I started playing with the low speed needle and was getting it to almost stay running when I throttled down. I then sold the plane it was mounted on . I have now installed it in my 40 size twist.Can someone please give me a quick refresher on setting up the low speed . I can't for the life of me remember whether to screw it in all the way and back it out 1.5 turns or what. Engine came with no manual. Thanks in advance Mike

[Wayne V]

Manuals are here http://www.osengines.com/manuals/index.html

[hifly2104]

Thanks for the links to the manuals. Well that took me to a manual that says the low speed is set at the factory .Use this setting until engine has been run and adjust in small amounts. Unfortunately someone else has been before me and its way out of whack. Somewhere in my brain I remeber something about a fuel line and blowing on it as the screw is turned until a small amount of air escapes. mind you this was on an entirely different engine and carb .Both carbs where two needle metered though. Anyhints guys.

[Wayne MIller]

Hi,

Hope this helps (see below). I keep adding to this so treat it as a work in progress. It is a collection of hints I have read on engine tuning from the different bulletin boards.

Let us know if it helps.

Fly4Fun,

Wayne Miller
========================
ADJUSTING 2-CYCLE GLOW ENGINE CARBURETTORS:

First make sure there is no air leaks in the fuel lines, make sure the fuel lines are not kinked and the fuel tank is not too far from engine. Ideally, the centerline of the fuel tank should be in line with the fuel pick up on the carburetor. The tank “klunk” pickup should not block fuel flow, that is, it should never touch the end of the fuel tank when the nose of the tank is pointed straight up (test when assembling tank or when tank is out of aircraft). Also if a pressure tap from the muffler is used, make sure the tap is not clogged and the pressure feed to the tank does not have any air leaks, nor is blocked. Make sure you have a good glow plug.

Remember, the high speed needle controls the engine at full throttle and the low speed needle controls idle and acceleration from idle up to 1/2 or 3/4 throttle – after that the high speed needle is in control.

First, reset your needle valves to an initial start position. Set high speed needle so it is 2 1/2 turns out from fully closed. Open carburetor to full throttle and use a clean piece of fuel tubing attached to the carburetor intake nipple, then blow gently into it with your mouth - listen for air going into the carburetor (it will be a “hiss”). If you don't hear air, back out the high speed needle valve a little and try again - keep doing this until you hear air passing freely. This ensures your high end needle is not blocked and will allow fuel (in this case air) to flow into the carburetor. If it doesn't, then try turning out another turn, or check for blockage in the line. Once you've verified the high end needle valve is working properly and allows air to be blown into the carburetor at full throttle, you need to set the low speed valve. To start, keep the same high end needle setting as above and close throttle to about 1/4 throttle setting. Note: Initial Low Speed Adjustment for Carburetors with Two Needle Valves (New Style)
On new style (2 needle carburetor) turn the low end needle valve so it is completely seated (meaning closed by turning it clockwise, do this gently and don't force anything). Now with the carburetor opened at 1/4 throttle setting, blow air into the fuel tubing and SLOWLY rotate the low end needle valve counterclockwise (to richen the low end mixture). Stop richening the low end needle valve when you first "feel", or more accurately, hear (a hiss) air leaking into the carburetor.

Note: Initial Low Speed Adjustment for Carburetors with Air-Bleed Adjustment (Old Style)
Gently tighten down the air-bleed screw until it stops and then turn out 2 full turns.

Then start the engine.

With the engine level, and running at full throttle, lean the mixture by turn the needle “in” very slowly towards the closed position, keep this up until the engine starts to slow down and wants to stop. Then quickly richen the mixture by opening the needle valve (turning it “out”) until maximum RPM is observed. If you notice very little difference when turning the high speed needle, you probably have an engine air leak, usually where the carburetor attaches to the engine body or at the back plate, this can usually be fixed by tightening, or with an “O” ring. Sometimes you may have to use high temperature RTV. This stands for Room Temperature Vulcanization and is like a silicon rubberized adhesive – you can get it at an auto supply store – they usually refer to it as a gasket sealer and you will need to get the high temperature stuff.

At maximum RPM, continue richening the mixture (slowly turn needle out) until you note a slight drop in rpm. This should be will be the normal operating mixture for the high speed adjustment.

There are two styles of low speed carburetor adjustments, that is, a 2nd low speed needle valve or an air bleed adjusting screw. If it is a low speed needle valve, the needle valves would be in line, and opposite each other or in the center of the throttle control arm. If you have a low speed air bleed screw would be to one side of the carburetor and will open and close an air hole.

These both are the only low speed idle adjustments and as such the low speed adjusting should be done with them alone, the high speed needle setting should not be NOT TOUCHED once you have adjusted it as described above.

LOW SPEED IDLE ADJUST SPEED PROCEDURE:

Close the throttle to the slowest steady rpm. From that, quickly open the throttle.

TOO RICH (too much fuel in mixture):
Did the engine run rough, burp, want to stop? If it did, the mixture is too rich. If it slowly died, it is too lean – see next section.

Note: If you have a low speed needle carburetor (new style), this can be leaned by turning the low speed needle in (to the right) about 1/16 revolution at a time.
Repeat (after first opening the throttle to clean out any excess fuel in the crankcase) until the change from low to high is immediate and clean.
If a lower idle speed is desired, close throttle a little and repeat the procedure.

Note: If the engine has an air bleed carburetor (old style) and the initial quickly opening the throttle indicates a rich mixture (as described above) the air bleed screw has to be opened a little. This will let more air in, try turning the air bleed screw to the left 1/16 turn at a time. Follow same test procedure as with the needle valve procedure when testing, that is, opening the throttle quickly.

TOO LEAN (too much air in mixture):
If the engine ran smoothly during initial quick throttle opening the engine, then slowly quit. The mixture is to lean.

Note: If you have a low speed adjustment needle, turn the low speed needle out (to the left to give more fuel) until the engine does not quit when the throttle is quickly opened,

Note: If the engine has an air bleed carburetor, and the mixture is too lean (too much air) then turn the air bleed screw in, to the right, to limit the air in the fuel mixture.

When proper low speed setting is attained the engine will transverse from low to high smoothly time after idling with no tendency to stop. If not increase the low speed rpm very slightly until. action is proper.

After the low speed has been set, return to the high speed needle adjustment and fine tune.

= = = = = = = = = = = = = = = = = = = = = = = =

Optional Tests

At full throttle pinch the line, it should speed up almost immediately, if it takes a while to speed up then it is too rich, if it doesn't speed up it is too lean. Now do the same at idle, keep in mind fuel is flowing slower at idle so the correct mixture will cause the engine to speed up about a second after pinching the fuel line. If it takes more than a second or so it is too rich, if less than a second or if it doesn't speed up it is too lean.

Now it should be able to idle at about 2500 RPM or less. And have good transition. If it does hesitate then observe how it operates, if it hesitates while spitting out a lot of fuel the idle is too rich and it must cough up that fuel before it accelerates. If no fuel then the idle is too lean. Now the richer high end is dumping fuel on a hot glow plug, often it can put out the fire, but if just lean enough it will hesitate. Some engines can fool you buy collecting a lot of oil in the muffler and dump it out when you accelerate making this difficult to judge. Even so a lean idle will usually cause the engine to pick up, then slow down, then accelerate, or quit. A rich idle will usually cause the engine to accelerate slowly or maintain a midrange speed a second or two before accelerating.

Other Troubleshooting:

At full throttle the engine runs OK with glow plug driver on, but when removed the engine runs rough, stops, or has a lot of smoke coming out of the exhaust. Caused by either old fuel, a bad glow plug or a glow plug with the wrong heat range.
Engine starts then stops. This usually means it is running off of the fuel you used to prime the engine. Look for fuel blockages such as: fuel filter clogged, carburetor clogged (check by putting fuel tubing on intake nozzle and blowing with carburetor at 1/2 throttle you should hear air at carburetor throat), lines inside of fuel tank bad, opening of the fuel tank pick-up “clunk” touching the end of fuel tank.

[hifly2104]

Thanks Wayne that was the intructions I had read somewhere else but hadn't saved . Will try and save them now so as to have in the future

[Wayne MIller]

Hi HiFly2104,

Glad I could help. Let me know how it works for you.

Fly4Fun,

Wayne