ro347

My Feedback: (13)

I have a new OS 1.20ax. Ive broken it in using the specified method in the manual for 2 tanks. I am using a Xoar 17x6 and 15% nitro with 18% oil. The issue Im having is that the high speed needle doesnt seem to make much change in rpm as you turn. Ive started it back at the 2.5 turns out as specified. Leaning doesnt change much after about 1 turn or so, and have to turn about 2 turns or so to get it to go 400 rpms richer. My numbers here are pretty rough, but my point is that the needle doesnt seem to be working the way Im used to on my smaller t strokes and other 4 strokes. I seem to have to make too many turns for very small changes requiring many clicks of the needle to get any change at all at some points. Will also note that when it seems the engine had peaked, it is actually still blowing lots of smoke out of the muffler(i say when it seems to peak as I reach a point where the rpms start to drop again, but still lots of smoke coming out of the muffler. Since rpms are starting to decrease, affraid of turning further despite smoke from muffler)

What could be wrong? What should I be checking? I have noticed that the HS needle doesnt sit in the the threads tight, and does have a little wiggle room. Im assuming this might be normal. i havent had a chance to compare it to my other 2 stroke engines.

At a total loss and desperate!

Any help would be appreciated. i really want to get it running at its best. Currently Im having to fly it at about 7900 rpms. Part of me thinks the rpms might be normal as they will increase with time, however the tuning process is very difficult and unable to tune with certainty.

Whats been suggested to me is the following:

The needle valve body might be damaged from possibly turning in too tight. Im not sure this is the case. Yes the needle has been closed, but not cranked shut. Wondering how I can check this - what should I be seeing when inspecting.

Another possibility is to slip fuel tubing over the needle and needle valve body in order to seal if any air leak is present. Just to note in regards to air leak - I dont not have any issues killing engine.

Thanks

Bax

My Feedback: (11)

First off, we'd say that you're using a too-large propeller for breakin. The engine is likely turning a too-low RPM, lugging it, which makes the needle impossible to get tuned correctly. Put a propeller on it that will allow it to turn about 8,000-9,000 RPM. Middle-8,000's is about where you want the engine to run. Too many people put a too-large prop on it and load it down, well below 8,000 RPM. This will cause the engine to run hot and to have fuel draw problems.

Try that, first.

Also, 2 fuel tanks' worth of fuel will not break in an engine. It may loosen it a bit so that you can fly it, but the engine won't really be broken in until it's had about a gallon or two run through it. We tend to run engines on the test stand for about an hour before we commit them to an airplane...more if the engine needs it.

O.S. suggests large propellers because they keep prop noise down, which makes everything quieter, overall. That's because noise is very strictly-regulated at flying sites in Japan. They almost always run better if you give them a bit more RPM.

ro347

My Feedback: (13)

Thank you BAX! I will try the 16X6. Hope that works and fixes the problem. Thanks

ro347

My Feedback: (13)

Today I swapped out for a Xoar 16x6 and am able to get 9000 rpms ready to fly.

I STILL HAVE A FEW ISSUES....

First I slipped a small piece of fuel tubing over the needle base. This seemed to help the tuning a little(tried this with the original prop first). Now Im getting the RTF reading of 9000 at 2 1/4 turns out. I notice that when you touch the needle, the rpms change a little. Up to 200rpms. Why is this? Is it possible that I have a bad valve body?(maybe the threads arent tight enough as I posted earlier that the needle does have some play in it) If so would OS replace this? Ive checked the needle on my OS 55ax and its a much tighter fit.

Also I have a knock at 1/3 throttle. I can blast to full throttle and back no problem, then takes 15 seconds or so and it comes back. What could this be?