2 needle opposed to 3 needle carbs  
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2 needle opposed to 3 needle carbs - 11/28/2004 4:01:17 PM   
Eagle Flyer


 

Posts: 617
Joined: 12/28/2001
From: Ida Grove, IA, USA
Status: offline 		I don't have any helicopter experience but was pondering this. If so many airplane engines have trouble with midrange, how about a 3 needle carb to fix it? Cost more sure, would it work?
On the other hand, I have tuned a lot of engines and all run good. I have never experienced the midrange thing as a permanent thing. Always been able to get rid of it one way or another. If it had some ones "permanent" or "design" problem I usually found it wasn't. Simply some kind of mechanical problem. Usually air leaks.
       Post #: 1

RE: 2 needle opposed to 3 needle carbs - 12/1/2004 2:03:15 PM   
Meesh



Posts: 1864
Joined: 1/31/2003
From: Dracut, MA, USA
Status: offline 		The only 3 needle carb I've ever dealt with is the one on my Thunder Tiger .70 helicopter engine in the TT EK-4 Monster Truck. The instructions tell you not to adjust it so I didn't.

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(in reply to Eagle Flyer)
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RE: 2 needle opposed to 3 needle carbs - 12/1/2004 3:23:53 PM   
DarZeelon



Posts: 7104
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: offline 		There are several other carburettors with a mid-range adjustment facility.

Many carburettors, for cost reasons, are produced with a simple idle needle taper (or none at all), presuming most users run their engine at either of two settings; full power, or idle.

This assumption is a very wrong one, to say the least.

Such carburettors will need a third, mid-range fuel control; the third needle.

Engines with more invested carburettors have a precision tapered idle needle, which precisely meters the amount of fuel at all throttle settings, to about 70-80% of full. Such engines have a better throttle linearity and the engine sounds 'right' at all settings.

Many OS, Magnum and Rossi engines tend to have too rich a mid-range, that causes these engine to stumble, following throttle setting changes after an extended mid-range run.

They will definitely gain from having a third needle...

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Dar Zeelon - ISRAEL - ddzeelon@gmail.com
MVVS - Jett - Nelson - Bolly - Mejzlik

(in reply to Meesh)
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