os 55 ax

[stuart macrory]

hi all i have an os 55 ax that is mucking me about, i have the engine fitted in a kyosho edge,problem is when in flight(never on the ground)if im flying at full throttle and then snap the throttle shut after a handful of seconds of the engine ticking over it will then cut and i have to perform a dead stick landing.i dont have much knowledge on tuning engines but a far as i can tell all is well.it throttles up smoothly etc

hope someone can help

could it be too rich bottom end???

[Former Member]

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[stuart macrory]

thanks eric,so would i be right in saying that to lean the top end you close and to lean the bottom you open?

[Bruce Richards]

I have had the same problem with my 55 AX in a Hype. I found that after running in it was necessary to lean off the low end by about 1/2 a turn may be a bit less. I have found it difficult to get a good clean pick up after a long ideal period. It only seems to be a problem in the air not on the ground. But I have found the key for my engine is to get the low end set right and it seems very sensitive to small changes.

Hope this helps

[flytilbroke]

My experience of glow and  my two OS 55 AX confirms the above advice.

[flytilbroke]

Just realised you mention after a couple of seconds, It is possible that in flight the "unloading" of the system may be leaning-out the low setting so that opening the throttle again makes it too lean to rev up. I would try leaning it out on the ground first though. Then if need, try just a slight bit richer than you have it at just now.

[Former Member]

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[stuart macrory]

sorry eric,i was asking, to lean the top end i know to screw in the main needle but the lean thebottom end do i screw out the mixture control valve? (botom end needle valve)

[Former Member]

[This posting has been removed]

[stuart macrory]

on my 55ax the 2 valve screws are right beside each other,but what your saying is that you screw both clockwise to lean and anti to richen?

[flytilbroke]

Stuart, you appear to be very confused as to what are the mixture screws. The AX main needle is just the same as are most of our engines, depending on the carbureter. Mine is rear mounted, also known as remote mounted.

The mid range / idle mixture screw is in the centre of the control arm assembly to which a narrow blade screwdriver is applied. it is fairly deeply inset, a bit more than on some engines. Did you not get a manual with it?

[stuart macrory]

yes the manual says the mixture control screw which im assuming is the low end needle is about 1/2 inch or less from the main or top end valve,the only other screw i can see is in the centre of the black plastic throttle arm which i thought was only for adjusting the postion of the arm.

[stuart macrory]

sorry if im causing any confusion

[simon barr]

Hello Stuart,

On the AX range , the main needle sticks out to the left like any other motor but the idle needle is the small adjusting screw just behind the main needle on the same casting.

To adjust the main settings, turn the main needle in or out (lean or richen), and to adjust the idle settings turn the small screw in or out (lean or richen), but by very small amounts as this needle is very sensitive.

[260 Flyer]

Just to remove any confusion!

Taken from the 55AX manual.

[flytilbroke]

That looks like it will solve the confusion. Better than I explained  Sorry Stuart.

My type of carby is as I said tho'.

Good engines,

[Simon Chaddock]

To follow on from Eric's advice, it is not a good idea to move a model engine throttle too quickly as fuel is so much heavier than air it reacts more slowly to the changes. This causes a rich mixture as the engine slows, usually not too much of a problem but it can put the glow out, and weak as the engine tries to speed up which can make it splutter and die.

Snap throttle response in petrol engines requires a sophisticated carb to over come this but fortunately methanol has a wider usable mixture range and adding nitro helps quite a bit more so model engines get away with (relatively) simple carbs. On a historical note the Rolls Royce "R" engine, as used in the Supermarine S6 racing seaplanes was noted for spitting unburnt fuel out of the exhausts when throttling back.

Of course one day electronic fuel injection will become cheap enough for models engines and the mixture problems should disappear, only to be replaced with unfixable electronic gremlins!

[stuart macrory]

so from where the engine is set now do you think i should try to lean it bottom end ever so slightly?

[Simon Chaddock]

It is very difficult to advise on a specific adjustment remotely so your best solution is to actually demonstrate what is happening to an experienced IC flyer. They will probably be able to tell whether the engine is cutting out rich or weak or is due to something else.

If this is not possible then I would suggest some simple flight testing. 

1. Close the throttle slowly and see if the engine ticks over OK for a reasonable period. If it idles ok then your snap closing of the throttle is the culprit. If it still cuts out after a few seconds at idle then your carb settings are suspect, but remember it could be other things.

2. Before you change the Mixture Control Valve you should satisfy yourself that the Needle Valve setting is correct (slightly rich) at full power as this will effect the mixture at all other throttle settings.

3. Only then should you consider adjusting the Mixture Control Valve but make sure you know exactly where it was before you start in case your adjustment makes things worse!

From then on it is just patient trial and error but always test any adjustment on the ground before you fly! 

[batcho99]

Yes Stuart, if it's no good you can always put it back to how it was, 1/8th of a turn at a time, clockwise to lean. Check your plug too, a nice new plug always helps, a no.8 will do the trick. Plugs get clogged up fast when an engine is rich.