Hi - I want to run my engine in right. It is an OS46FX. I know I am meant to run the engine REALLY rich by getting it to 4 stroke and then leaning it slightly so it 2 strokes again.

My problem is that I am not sure I am picking up when it is 4 stroking. I have read that it should be growling and deeper etc but I could not detect a change no matter how rich I went. The engine would just stall without 'growling' imho.

Could someone email me a audio files (mp3, wav, whatever) of a 2 stroke engine that is 2 stroking, and is then 4 stroking please?

Hope someone could help

Let's start from the beginning. It sounds like this is a spank brand new engine. What prop, plug and fuel are you using?
Once started and tuned, what rpm are you getting?
If this is a non-ringed engine (I'm not sure), you don't want to run it REALLY rich anyway. Let me know and we'll get started_bob

If this is an ABC engine [and I think it might be] I suggest you read some of the stuff Dar Zeelon has posted on RC Universe about 'running in'.

the 46fx is an abn motor.. you dont want to run it really really rich. if you cant tell when its 4 stroking.. add a few clicks of throttle trim to cause it to idle a tiny bit faster and you will be able to tell. instead of sounding nice and smooth.. it will sound like its "missing" kind of like when your car isnt running right. that is 4 stroking on these motors. do a search for .46fx and sort thru all the posts and im sure (and i place a dollar on it) that you will find what your looking for!!! or take a look at my website under engine tip page if you still have trouble!! good luck. its a good running motor but you have to have patience with it!!

Running an ABC (or ABN) engine rich will ruin it. So if anyone has used those OS instructions, as far as I'm concerned, they should write to OS and demand a replacement engine.

ABC engines have an Aluminum piston in a Chrome plated Bronze sleeve (ABC), or Aluminum piston in a Nickel plated Bronze sleeve (ABN) which the OS's actually are.

Because of the different rates of expansion of the piston and sleeve, the sleeve is bored to a taper making the piston/sleeve fit "squeaky" tight at top dead center. (Sometimes they're so tight it's difficult to turn them over when cold.)

IF you run one of these "4 cycle" rich, the excess oil/fuel will not allow the engine to get to operating temperature, and the piston will rub against the sleeve causing excessive wear. The end result will be too little compression for a good, powerful engine.

Proper break in? Tune the engine until it's completely 2 cycling (at full throttle obviously) but not peaked, and run it for 3 to 4 minutes. Shut it down and allow it to cool enough to touch the cylinder head.

Restart the engine and repeat. Run through at least 2 to 3 tanks this way, then you can fly it. Do not lean the engine much beyond the break in setting until you've run a couple more tanks through it.

Of course, you never run an engine at "peak" RPM, always at least 300 - 400 below peak. (They lean more in the air when the prop unloads.)

You never set an engines primary needle valve at idle though. You really can't determine it's high end setting, rich or lean, unless you're in the "high end" (full throttle).

Setting the low end, or idle mixture is done at low throttle; set with a second needle valve or an "air bleed" screw depending on the engine. Changing the idle mixture will change the high end setting a bit, so be sure to re-set the high end. (But high end needs to be set first, then low, then recheck high end.)

I know it's difficult to know what "rich/lean" sounds like without knowing what it sounds like, but I don't have a sound file, sorry.

But at Full throttle (as I mentioned), a lean-ish needle setting will sound like a continuous fairly high pitched 'whine'. Four cycling sounds like the whine is constantly breaking into a 'burble'.

Nyee-ee-ee-ee-ee-ee-ee-ee.... is as close as I can "write" lean.

Nyee-ee-arl-ah-ee-ee-yahl-ee-ee-ahl-abl-yee-ee-ee... is as close as I get to "rich".

You really have to sound it out a couple times quickly, but I hope it helps.

Good luck, and the easiest way to do this is find help locally if possible.
Dennis-

i am confused i thought a 2-stoke engine always ran with only 2 strokes.....

Actually no, they don't if the mixture is very rich. No one's absolutely certain why it happens but they definitely miss a beat, fire, miss, fire and so on. If you go to the web page I do for my club you can see a graph (derived from cylinder pressures) of an engine in 4 stroking mode. It's a curious phenomenon and has a few surprises.

http://www.holdfastmac.com.au/instanttorque.html

i guess i never really payed attention, i always get my engine idling good and good on the high end, then go, never noticed