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(This applies to two needle heli carbs, three needle carbs are obviously done differently.)

On Fri, 2 Aug 2002 07:56:24
>  Tom D wrote:
> >Hi Jason,
> >
> >A quick note of thanks for helping me tune up my engine.  It was a great learning experience and the payoff is very high.  I've been trying to "random walk" my way to a well tuned engine, and it obviously hasn't worked.  I hadn't understood the need to do much low needle adjusting and I've not thought of it as important to the result.  It's important to have a process and know what you're looking for and (hearing acuity notwithstanding) I think I can replicate this in the future.  Here's my recap:
> >
> >Presuming pitch curves are appropriate and balanced for the engine/blade sizes...
> >1) Climb-out test:  From a rich starting point--lean the engine until the full climb-out has the engine slightly accelerating the blades and the engine doesn't sound rich (can't really describe that--I mostly can tell when it's lean.)
> >    -This means that as the high end needle is leaned up, to keep the middle from leaning out you will likely need to offset via richening up the low-end needle.
> >
> >2) Hover test: Starting point has fuel line pinch "lag" of around 4 seconds when at idle--not instantaneous as mine was.  Richen up idle.  Then the hover mix is set using low end needle.  [When hovering, heli should be smokey and smooth. Watch for the tail kicking if the engine is running rough.  If it's kicking but there is not much smoke, this is a lean indication, richen up the low needle until the heli hovers smoothly with no tail kicking.  Too rich in hover almost never happens with this type of carb, so if it's not smooth it's probably lean]  Don't touch high end needle at this point.  There are pretty easy visual cues here--i.e. smoke at idle is pretty easy.  Sound cues are not too bad--particularly if too lean.
> >
> >3) Repeat Climb-out test:  Low end needle changes from the hover test may require some re-adjustment of high-end needle.  For example, leaning out the low end needle may require making the high needle a couple of clicks richer in order to keep the middle of the throttle curve in line.
> >
> >4) Throttle curve adjust:  Hover is easy enough, full throttle is obviously easy.  Big thing is the zero pitch setting which is tested by full forward flight transitioning to zero pitch "gliding."  Throttle curve for zero point should have engine speed pretty stable, not sagging, and not racing.
> >
> >Not very complicated as a process--the key is in the execution, so we'll see how I do with the OS50.
> >
> >Thanks again,
> >Tom
> >
 
 

email me:  jbond007 at lycos.com