I need to lower my idle RPM on my OS 46AX. How would I go about that? Would I be leaning the low needle or richening? The idle is currently around the high 2ks(or so) rpms and very reliable(doesnt quit). Two problems....One- As I start to taxi....once i bring the stick all the way down...the engine continues to pull and running around the runway...and Two- THe engine doesnt seem to be 100% consistent on its idle rpm. Lets say you rev the stick 5 times....2 of those times the idle will come down low....the other 3 it will stay a bit higher. What am i missing here?

You do not lower idle by changing the mixture. You lower the idle by... lowering the idle!! Use the trim on your transmitter, and if it is already bottomed out, then readjust the linkage to get a lower idle speed.

Once you have set your needle valve for optimum high speed operation, you leave it alone. You want the high speed (full, wide open throttle) to be set just on the rich side of lean to provide lubrication, and leave it alone for that day. It changes daily due to weather conditions, pressure, humidity, and so on, so set it before flying the first time and leave it. Adjust your idle, as I said, by the trim lever on your transmitter or by readjusting the throttle linkage.

what cgretired said is correct except that some carbs have an idle stop screw that stopps the rotation of the barrel ,sometimes this has to be backed out a bit to allow the barrel to rotate more.

If the throttle is inconsistant you may have a bind in the controls. The idle speed is set with the linkage/transmitter. Mixture is set with he screws.

the 46AX doesn't have a stop.

I wonder if this means the throttle linkage may be sticking intermittently?


Edit: Bruce beat me to it!

What these guys said about checking your throttle linkage is especially true if you are using a cable rather than a pushrod for your throttle. If your cable sleeve is allowed some lateral movement, then it can cause inconsistency in where the throttle ends up at the same radio input.

Well...when i bring the trim lower it dies. I will check the linkage again. Thanks!

OK, a relatively new engine will NOT idle at it's minimum speed until it's been fully broken in and loosens up. Secondly, if you are at the minimum throttle setting before it quits it MAY be too rich. OS tends to ship a bit with the idle a bit on the rich side to protect the engines. Again, the engine needs to be almost completely broke in before adjusting. How much has this engine been run in terms of gallons/tanks/hours or whatever?

Its not the only thing I fly...but it has to be AT LEAST 2...more towards 3 gallons on this engine.

Bruce: The possible exception to that is the OS 74 AX I just bought for the Protege. I started it up yesterday, ran it about 2 minutes at a high idle, then gradually increased it to full throttle with a very rich mixture and ran it that way for another several minutes when I leaned it out for about 10 seconds then ran it down to a high idle again. Just for curiosity, I reduced the throttle trim from high idle to a very slow idle of about 1800 RPM. It stayed there idling along very nicely.

It did hesitate a bit after that when going to full throttle, but it never stalled out.

I ran it through the rest of the tank and then refueled it and put the plane in the air. It never once hesitated during the next full tank burn, and I did several touch and goes after about 5 minutes of fam-flying.

A great engine, probably an exception to the rule when it comes to new engines, that's for sure.

An idle in the high 2Ks is actually a typical low idle. What it sounds like is he's flying off an asphalt or concrete surface, and can't keep the plane from rolling.

If this is the problem, try putting some fuel tubing on the axles to increase the drag of the wheels. You'll still be able to pull the plane for take off, but it will help hold the plane in place while idling. You may also need to consider flying with someone to help you hold the plane.

Brad

I can vouch for that. When I was review the OS 75 AX (it's one better than your "74" Chuck ) I broke it in on the test stand. I primed it until fuel reached the carb and the then the engine started on the second flip. First tank of fuel and it would idle reliably at 2500 rpm with no problems. I'm really impressed with this new engine.

Ken

Yes...we are lucky enough to have a runway. I guess ill give the rubber brakes a shot.

Ken

Hi!
Set the idle rpm to about 2000-1800 rpm and you (Your airplane) will have no problem standing still on a paved surface.

How many gallons till you can consider an engine broken-in?

I have yet to see a 46 2 stroke that would idle reliably 2000-1800 rpm.

2500 is usually my lowest reasonable target for an idle in that size.

Brad

I hvae a .50 that on its forth tank of fuel (6 oz tank) without touching the low speed needle would idle at 1800 rpm and it is an insainly tight engine

I have a couple of these .46AX engines. Very solid running engine once tuned properly. I usually idle mine around 3000 to 4000. Guys at the field recommend 4000 for idle. I've dropped mine a little lower at idle since these run as well as they do... depends on the prop size as well(flywheel effect). Spend some time getting familiar with the mixture control(idle needle) and needle valve(high end needle). I've got mine tuned so there is zero hesitation to wind up from idle to WOT after sitting a minute or so(no loading up) and run them 200rpm below max lean RPM and it stays tuned like this unless I change fuel. It's fun tuning engines I think to eek out that last bit to make it run smooth.

somegeek

4000? My plane would prob take-off! J/K

How do you land the plane at half throttle? 4000 RPM? Are you sure you are using the 2 blade setting on the tach rather than the 3 or something? All my engines (three OS .46's, one OS 50, three OS 1.20 AX's and my new OS 75 AX) idle below 2500, and this new OS 75 AX idles perfectly at about 1800.