Hi All,

Firsly I was going to break in an OS46, that was in a bi-plane. But since I am a beginner (long time fan and hobbiest .. but with low flying experience) , i decided to get a 25 size trainer. Not very big, but a nice trainer with ailerons.

Following my limited OS experience of break in, as well as some friends info, I have started with a rather rich mixture and step by step bring into leaner (not too lean) adjustments. Well, i haven't counted how many fuel tanks i've burned, but it has to be close to 4. Now, it already idles really well, and can gp about mid range very smoothly .. when I open it up to about 60% or more, it is still not very stable. Also, when i lift the plane tilt it up etc it almost stalls .. unless I quickly bring it back to normal position.

Just wanted to know, does this sound ok so far, should I just keep doing what i am doing for a couple of more tanks of fuel ? Also, I adjusted the linkages a little as the servo travel with the set-up was gpoing too far, even slightly bending the pushrod. I am using Top Power Fuel, Nitro 15% ..

Thanks for any comments on simple, safe and effective glow engine break in procedure,

It is most likely "broken in" by now (if it is an ABN engine?), but it sounds to me like it is running too lean at high revs. The main needle should be set att full throttle only and you should be able to point the plane up without the engine dropping in revs. If the engine cannot hold full thottle, then it is not fully broken in. If this main needle setting makes to low end too rich then you correct that using the airbleed screw or second needle, depending on what carb it has.

I've only adjusted the main needle valve one way or the other so far at about 30-40 % full throttle, to make it run smoothly .. I guess only slightly rich. And from idle to 30-40% range, it runs really smooth and well, but at 50% or higher it "looses" its timing / adjustments almost immediately. That's why I didn't think it was the needle valve adjustment issue .. although I will try to make it richer, while pushing it near full throttle next time.

I do see some significant improvements during the last several runs, so it may also be close to break-in but not completely yet.

The engine is a Magnum XL 25A. It only has the one main needle valve, and 1 screw (for air bleed). I've never touched that screw yet.

The Magnum has a twin needle carb as far as I know (?) and the low speed needle works from idle up to about 50-70% while the main needle sets the top range.
The main needle should be set at full throttle only, if then the low end is too rich that is corrected for by using the low speed needle. So you need to get the engine running slightly rich at full throttle, by adjusting the main needle, only then should you worry about the running below 50% throttle and you fixed that with the low speed needle. The two needles are linked so it is important to tune them in the right order and at their corresponding rpm range.

Either your engine is not a XL25A, or you have not seen the low end valve.
The low end should be adjusted by you.

http://home.wanadoo.nl/pereivers/engines1.html

If you don't have the manual for the engine, this one will serve you as a guide for manufacturer's recommendations for break-in and further adjustment:

http://media.hobbypeople.net/manual/210756.pdf

You have the high speed needle adjusted too lean. Open it up about 1 turn then start the engine and run it full throttle. When it has had time to warm up turn the needle counterclockwise to richen it till it sounds all blubbery then slowly turn it clockwise till it starts to scream. Now slowly(very slowly ) turn it farther clockwise till it slows down , now you have learned where the needle goes lean. So turn it counterclockwise till it starts to scream again, a little more till the rpms slow down about 200 rpm and that should be your setting.
Now adjust the idle mixture to where it doesnt stumble when the throttle is opened.

Appreciating all the above infos and suggestions. Thanks ..

Based on all above, my low speed needle valve should be hidden behind a blackened 8mm needle plug (not to far from the fuel nipple). Then, there is an idle mixture screw (small flathead a assume, ), that you access through a hole on the side of the throttle arm.

Will try your above instructions as soon as the rain slows and write the updates. If what I wrote seems off, let me know.

Thanks again,

Please read carefully the break-in procedure specified in the manual supplied to you by LNEWQBAN. VERY similar to OS, the procedure involves starting up then advancing to FULL THROTTLE in a very rich condition then slowly leaning out the high speed needle. I suspect this is not how you have been proceeding.

Once the engine runs at full throttle at high needle settings from rich to lean, set that needle at a speed a little below top rpm and THEN adjust the low speed needle. Finally, REadjust the high speed and you should be ok.

Best of luck!