I have an OS 55 AX. Im having trouble when going from idle to full throttle. It wants to die or hesitate before spooling up. Ive run about 6-7 tanks of fuel through the motor. I was told to turn in (lean up) the mixture control, I turned it in almost a quarter of a turn and this did help some but, Im still getting the some hesitation and also a very very wet puddle from the exhaust. This would seem to still be rich but Im afraid of over heating the motor. I have the needle set at out about 2.25 turns which is per the manual. Thanks for any helps or tips.

Sounds like you need to lean out the mixture control valve instead of the high speed needle.

Open up the idle jet about 1/2 turn, or better yet set it to the factory default setting. Same for the high speed. Now get the engine running and let it warm up a bit. Go to full throttle and lean out the high speed until it starts to drop RPM then go back rich about 1/2 turn. Idle down as slow as you can and at this throttle setting, lean the idle for maximum RPM. Go bach and do the high end one more time, go back and do the low end again. Now when you punch it, if is heasitates and stumbles, the idle is still a bit rich go about 1/16 turn at a time lean until it jumps to life. It it dies when you punch it, the idle is to lean, so go rich 1/16 turn at a time until you get the good throttle response.

Check for any air bubbles in the line. If you see any, you have a air leak and it needs to be address first.

The above setup addresses the idle and transistion, but isn't the peak performance for the engine. It is close though. I would run the high speed a little on the rich side for a few more tanks before going for top performance. It will give you good reliable performance though.

Don

There are 2 needles to control mixture on the 55AX, and most other glow engines.

There is a high speed needle, this one's obvious. Large knurled knob to turn, either on the carb, or remote on the backplate. This one tunes full throttle performance. This one is adjusted only at full throttle, to a couple hundred rpm's rich of peak rpm's (a minor, but distinctly audible drop in RPM's). Basically, with the engine running full throttle, you'd first rich this needle to verify that you're on the rich side of peak to start with. The engine should slow as you open the needle slightly (a couple clicks should produce results). Now, slowly, click by click, lean the needle. Engine accelerates with each click, and then stops accelerating. Go any further and it'll quit. Now open the needle a couple clicks until you hear that slight, but distinct reduction in rpm's. I use a tach personnally, and set the rpm's 300 below peak. I find it more repeatable that way. Get used to this part of tuning, it is typically adjusted at the start of each flying session. This is not the needle you need to change to fix acceleration hesitation.

The second needle is the low speed needle. If you look at the throttle arm, you'll see a small flat head screw down inside the arm's center. This is the LS needle. This is the one that you must adjust to get better transition. It affects the mixture at idle thru mid throttle. It is adjusted with the engine OFF (too close to the prop to be safe with a screwdriver). Once correctly set, it won't need changing unless the fuel is changed or the engine is wearing out. To adjust, Start the engine, run it wide open a few seconds, then go to idle. Allow the engine to idle for at least 30 seconds. Whack the throttle wide open. If the engine spits, coughs, sputters and then either dies or finally accelerates, lean the LS needle a tiny bit (screwdriver blade slot width sort of amounts) If the engine dies immediately, no spitting, coughing, no puff of smoke from the exhaust, it's too lean, rich it a tiny bit. Repeat until the engine will accelerate cleanly after idling at least a minute.

The HS mixture is typically tweaked a bit to be sure after the LS is set, just do the HS thing again. The LS needle does have a minor effect on the HS mixture is why.

Once you've successfully completed the above steps, you should have an easy starting engine that doesn't deadstick, idles smoothly all day long, and accelerates eagerly.

Good luck,

J

It's most surely caused by your low speed needle being out of adjustment.

I'm a big fan of the "pinch" test for setting the LSN.

Engine warm and at idle, pinch the fuel line ahead of the remote needle (if you have one).

If the engine shuts down, you're too lean.

If the engine does nothing, you're too rich. You can verify this by pinching and holding the line..... The more rich you are the longer the engine takes to increase speed.

The engine should increase speed slighty, that's perfect! That should get you very close. If you still have a small problem with transition, refer to the instructions mentioned by others for tweaking after the pinch test. But mine's always been dead-on.

A couple other things to keep in mind as well:
First off, the settings mentioned in the manual should be concidered starting points.
Secondly, there are a variety of factors that will make it necessary to deviate from the factory settings. Weather, fuel tank location, pressure in the fuel tank, glow plug, the fuel itself, and prop size just to mention a few.
Equally as important as the carb settings is the location of the fuel tank. The closer the better, and the spraybar in the carb should line up with the center of the tank. If it's hot today and you tune your engine to run perfectly, As the temperature starts dropping in the evening, you'll find that the engine is running a bit richer. If your prop is too big or the pitch is too steep it will give the effect of being too rich. If the prop is too small, it will probably overheat pretty quick.

thanks to all very much... will print and get at it.... sure is nice to be a part of such a great group... thanks again