2 needle opposed to 3 needle carbs
11-28-2004, 11:01 AM
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2 needle opposed to 3 needle carbs
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.
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.
12-01-2004, 09:03 AM
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RE: 2 needle opposed to 3 needle carbs
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.
12-01-2004, 10:23 AM
#3
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RE: 2 needle opposed to 3 needle carbs
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...
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...
