How to extend high speed needle?

[Jack_K]

The high speed needle on my OS 46AX (not the AX II) is inside the cowl and I am unable to adjust it when the cowl is screwed on.

Is there any way to extend the needle?

[PappaBear]

RE: How to extend high speed needle?

The high speed needle on my OS 46AX (not the AX II) is inside the cowl and I am unable to adjust it when the cowl is screwed on.

Is there any way to extend the needle?

Hello Jack,

In the end of the needle you will find a small hole and to one side there should be a allen headed grub screw. Insert a suitable length of wire into the hole and tighten the grub screw. Make sure the wire is long enough that it will exit the cowl and it is long enough to make adjustments to the setting. Making a 90º bend on the end of the wire will make it easier to turn and will also give you a reference mark.  Make sure the hole on the cowl is large enough that you can screw the needle into the carb after you refit the cowl to the model.

I hope this helps you.

Martin.

[fhhuber]

RE: How to extend high speed needle?

I recently saw a suggestion of finding a socket head screw that will fit the hole in the needle valve. Using that instead of a wire you can use a long allen wrench to adjust the needle and you don't have to work around the long wire when putting on or removing the cowl. You also won't need a large hold to fit the needle through. Just leave the needle in the carb.

I wish I had heard of that idea long ago...

[WintrSol]

RE: How to extend high speed needle?

I recently saw a suggestion of finding a socket head screw that will fit the hole in the needle valve.  Using that instead of a wire you can use a long allen wrench to adjust the needle and you don't have to work around the long wire when putting on or removing the cowl.  You also won't need a large hold to fit the needle through.  Just leave the needle in the carb.

I wish I had heard of that idea long ago...

A ball-tipped Allen wrench will work better than a straight one; a Torx wrench with a slight taper ground on the end will also do a good job.

[Konrad]

RE: How to extend high speed needle?

Please be aware that adding an extension to the needle valve can cause fuel mixture tuning issues. This is because the added overhang can start to vibrate allowing the needle to move around in the jet. If the the needle moves around enough that the boundary layer of the fuel jet and needle interact this will effect the fuel flow rate through. the jet. This phenomenon is known as “false needling” in the high performance engine world or hysteresis in engineering circles. 


It is best not to add the long wire extensions if possible. If you must try to support the end of the wire with a grommet through the cowl that gives a snug fit on the wire. Brazing the head of an allen cap screw is much better as far as the operation of the engine. But it is not considered safe to use tools around a running engine. Finding the lean reversal point can be a pain if one does not use a running engine to find it. You should use a tach and record the readings and needle positions to find the lean reversal point. Barring that be very carful with any tools around a running engine.

I think we go into details about this in these threads;
http://rctruth.com/index.php?topic=1741.0  at the bottom of the page.
http://rctruth.com/index.php?topic=1750.0 

All the best,
Konrad

P.S. The needle holder on the OS engines often have 5 times less clearance than some other brands. This results in better needle control (less likely to give a false needle).
P.P.S. Use silver bearing solder to braze the allen head of the cap screw to the needle.

[wrongroad]

G'day gang,
This may well not apply to the needles on an aircraft engine but this is how we used to extend the needles on the Walbro carby fitted to the Yamaha KT100S Go Kart engine that I raced here in Australia.
We used multi strand wire similar to the wire used in the hand brake of a push bike and brazed it onto the top of the high speed needle. We used heat shrink around the wire to allow the cable to be flexed [bent] and stop the wire from unwinding.
Later versions were much better and the commercial units even had plastic covering and a t bar with a pointed end to help a driver know just where the needle was set.
To prevent vibration, we used tie wraps to hold the needle to the low speed needle. The low speed needle was left as factory to help with identifying the high / low while racing.
I was going to say the use of a grommet but that has been taken care of already.
If this is of any help that will be good.
I fly electrics but I have made the suggestion to pilots in my club and a couple of them have used the idea with success.
Of course you keep the wire as light as possible and still maintain enough stiffness to do the job.
Regards and respect
Daryl

[benjack71]

The high speed needle on my OS 46AX (not the AX II) is inside the cowl and I am unable to adjust it when the cowl is screwed on.

Is there any way to extend the needle?

Everything you heard is good advice. I just want to add, speaking as a person who is into fast and easy due to my lethargic and lazy character. I normally use a section of push rod, cut to the length needed, and insert it into the hs needle hole, then tighten it into place with the allen screw. I dont know how much length you need, but a t handle works really well to!