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Old Nov 27, 2013, 09:29 AM
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SayCheeze's Avatar
United States, TN, Martin
Joined Apr 2013
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Question
Mixture Needles

I'm new to nitro, and read a great explanation here on RCG, of how to set the low end, from idle to 3/4 speed, and high from 3/4 to WOT, but which one is which on the engine? He mentioned that lean = taking fuel away, and rich = adding more, and I understand that statement.

I have an OS 15, 20, and now a 40. The only one in use at this time is the 15.

I would think one needle couldn't affect both settings, low/high.

Correct?
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Old Nov 27, 2013, 10:55 AM
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United States, WA, Port Angeles
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Quote:
Originally Posted by SayCheeze View Post
I would think one needle couldn't affect both settings, low/high.Correct?
yes they do! if you open the high end( richen ) you must close the low end, ( lean out )

some people will call it "walking the tight rope"
I will try and get the engine running as good as possible with the high needle first!

then adjust the low end for best idle and throttle response,

again with the high end, now pulling the nose vertical,

then check and retune the low end if needed, if so then double check the high end!

P.s. the high end needle is usually the one most easily reached, and the low end usually has too be tuned with a small screw driver.

the low end needle usually takes very small adjustments
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Old Nov 27, 2013, 02:08 PM
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United States, TN, Martin
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Thanks whisky...

I'm kind of confused. Not based your reply.

Based on what a fellow told me today, that I bought a plane from. He fly's RC's and Ultra Lights.

He told me to only concern myself with that one needle. He said basically, run the throttle wide open and adjust it until you hear it's top end performance, and then "rich" it a tweak until you hear the motor pull back a WEeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee bit.

He said that point, your ready to go.

BTW, the plane I bought was a 1/4 scale job.. GULP
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Old Nov 27, 2013, 02:38 PM
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Letchworth, Great Britain (UK)
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Originally Posted by SayCheeze View Post
... He told me to only concern myself with that one needle. He said basically, run the throttle wide open and adjust it until you hear it's top end performance, and then "rich" it a tweak until you hear the motor pull back a WEeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee bit.

He said that point, your ready to go....
He's right, up to a point

If you adjust the main mixture needle like he describes, and check that the engine doesn't die when you lift the nose up to vertical, the motor will probably run nicely at half throttle and above.

The reason for the low-end needle is to ensure that the engine also runs smoothly at low throttle, and picks up smoothly from idle when the throttle is opened.

So, after you've adjusted the main needle for best rpm, and then backed it off a little, pull the throttle down to the slowest you can idle smoothly, and then open it up again quite quickly. If the engine coughs and splutters and then slowly picks up speed, it suggests that the low-end needle is too rich, so close it down a tiny bit and repeat the test until you get smooth, almost instantaneous, acceleration. If the engine simply dies (or nearly does) when you open the throttle quickly, the low-end needle is too lean, so open it up a little, and repeat.

After you've got the low end right, you'll need to go back and check the main needle. It will only need a little extra adjustment, if any, after you've done the low end.
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Old Nov 27, 2013, 02:45 PM
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I will assume then, that we are talking about a previously tuned engine!

and again I will assume, that the plane in question, is from around your area! as in not much change in altitude!

then yes you probably could get away with just adjusting the high end! AND with that said, "as long as it doesn't take too much to tune the high end" then the low end should be fine!

tuning an engine by ear has been done by me and others since the beginning, and yes close the needle till the engine starts too slow down " you are lean " now slowly back the needle out, and find the highest point that it will run!
now is the critical part, slowly back the needle out some more, till you hear a change in the RPM's

at that point, raise the nose of the air plane, if the RPM's stay the same, then your good too go, if it rev's a lil and starts too die, back your needle out some more!
I personaly have never had a plane get richer from raising the nose! just saying!
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Old Nov 27, 2013, 03:04 PM
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United States, TN, Martin
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Thanks guys...

Practice is what I need with a nitro guy on my side. I'm new to nitro, and I'll be wreck as it is, just getting the plane setup, much less getting it in the air...

Appreciate the info...
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Old Nov 27, 2013, 03:12 PM
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"you can do it"
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Old Nov 27, 2013, 06:42 PM
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USA, MO, Ozark
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print and save this reference

here ya go http://www.rcuniverse.com/forum/begi...ml#post8844213
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Old Nov 28, 2013, 08:06 AM
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United States, TN, Martin
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Thanks folks..

Appreciate the link Oz

I think the size of this plane scares me some, even though I'm sure she's a gentle giant.
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Old Nov 30, 2013, 08:17 PM
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United States, IA, Rockwell
Joined Jul 2011
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Quote:
Originally Posted by SayCheeze View Post
Thanks guys...

Practice is what I need with a nitro guy on my side. I'm new to nitro, and I'll be wreck as it is, just getting the plane setup, much less getting it in the air...

Appreciate the info...

Now you're talking. I'm sure there are several who will be willing to help you.

Ken
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Old Dec 10, 2013, 10:50 AM
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winston mo
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It really depends on your carb. Is it in fact a twin needle or is it an air bleed carb.
An airbleed carb has a hole in front of the carb that allows air in when the barrel is closed to partialy opened.
There is a screw on the side of the carb that controls the size of opening on the hole.
This keeps the engine from going rich at the lower to idle settings. I set the airbleed after the HS needle and then set the airbleed where the motor doesn't load up at an Idle and for transistion.
The twin needle both needles control the amount of fuel. One at below 1/2 throttle and both at full throttle.
I adjust my LS after I set my HS. I set my LS for transition. If the motor dies when going form idle to wot then I richen the ls, if it hesitates then I lean it. making very small adjustments
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