OK, I have a Hobbico Superstar RTF. The whole box sat in an attic for about 6 years brand new. Now, I have about 60 minutes breaking in the OS 40LA engine on the ground, but it seems to have a rough idle. The engine at idle without the main wing on, the plane vibrates and the tail feathers vibrate like crazy, very uneven "4-stroking," if I understand that correctly. So I put the wing on and that seemed to stop the tail feathers from vibrating. This plane has been in the air one time at the hands of a veteran who I asked to trim it out for me, no poblems. But tonight just trying to run another tank of fuel through, I left it alone for several minutes at idle which was a bit irregular and then it died which could have resulted in a deadstick had it been in the air. There was still 1/4 tank of fuel. Otherwise throttle responds fine through full RPM.

Is this a break-in issue, or do I need to mess with the low speed idle? If so how? I haven't changed the factory needle valve settings. Just as comparison, I bought an old trainer with a well-broke in Magnum 40 and it purrs at idle all the way through full throttle.

Your description is limited but my bet is that the idle is rich. If it hasn't been adjusted since new the MFG USUALLY ships them set on the rich side to protect the engine against a lean run.

So, what do I do? I'm familiar with the main needle valve, running a bit rich for break-in, but how/where is the idle adjustment?

Assuming that I am correct. You need to lean the engine. This is an air bleed carb and the idle mix screw works opposite to most "standard" carbs. There is a small hole in the front of the carb that lets in air to mix with the idle fuel. There is also a screw that comes in from the side that PARTIALLY blocks this hole and regulates this air flow and thus the MIX. Turning the screw CW closes the hole makes the mixture more rich. Conversely turning the screw CCW opens the hole and leans the mixture.


ONLY MAKE SMALL (1/8 TURN) ADJUSTMENTS OF THIS AT A TIME. THIS IS VERY SENSITIVE.

Bruce-Thanks for the good advice. That screw looks way too close to the spinning prop so must I try to adjust it running, or OK to adjust it 1/4 turn at a time not running? Also, I only have about 60 minutes on breaking in this engine, is it safe to lean out the idle now?

One more question, there is a screw on top of the carb of the OS 40LA, but I assume the idle screw I need to adjust is the one on the side with the spring under it, right?

STOP the engine and make 1/8 turn adjustments. It would be easy to go right past the correct point if you make larger changes. Try to remember total changes made so you can go back to the starting point if that is decided to do for ANY reason, Normally the hole should be ABOUT 1/2 blocked.

OK can't wait to try this tomorrow. Meanwhile we'e supposed to get 2 inches of snow tonight here in KC. LOL! But Sunday should be 60 so it won't last and I'm hoping to meet a trainer at the field Sunday afternoon. Spring in the midwest! I like to say we only have two seasons here, winter and summer, and about 6 days inbetween.

OK Everything seems to be working OK, but when it's idling, if I lift the plane to vertical while idling, it runs for a 5 seconds then dies. At full throttle and vertical, no problem, only at idle speeds. Does this mean the idle is too lean? Or is this normal for idle to die when vertical?

It's NEVER normal to die. You may have gone too far to the lean side. These air bleed carbs are VERY sensitive PIA's.

So in theory I need to turn Idle richer until it doesn't die when vertical? Another symptom is that when I back down the throttle to idle (not including the trim to kill it) it gradually slows down over 15 or 20 seconds. Still a fairly rough idle. Could it be it's still too lean? As I turn the screw I noticed it turns very easily almost as if vibration might have got it out of whack in the first place.

I suppose the next step might be to RTFM that came with it to set everything back to factory reccommended.

sounds to me your messing around with an air bleed carb low speed screw when the HIGH SPEED needle is what is important. true , the low speed needs adjustment BUT the airbleed is often not as sensitive as many think. it is the TN two needle carbs with low speed MIXTURE control that are very sensitive. case in point; some air bleeds have to be drilled out the next drill size inorder to have any effect at all.high speed needle too lean.

This being a beginners forum, its important to get the correct information out.

First, any plane at idle, held vertical for several seconds, is going to die. There isn't enough exhaust pressure and suction to draw fuel. The plane is never going to fly in that position anyway (at least not at idle).

The way to check low speed mixture is not just to let it idle. Determine you're lowest reliable idle. The plane should be able to hold that idle speed for a few minutes. You're looking for an idle speed around 2500-3000 rpm. Your lowest reliable idle may be higher than that until you get the tuning adjusted. Adjust your throttle trim as necessary to get this idle speed set.

Let it sit for about 30 seconds. Punch the throttle. If the plane hesitates, and then runs up, the low speed mixture is rich. If the plane goes to full throttle without hesitation, you're good to go. If the plane hesitates and then dies, you're to lean.

You can also try the Pinch test. With the plane idling, pinch the fuel line off. If the idle speed rises slightly before the plane quits, you a little rich on the low end. If the idle never changes, you're probably close. If it dies immediately, your probably lean.

The punch test more accurately simulates flight conditions, and is my preferred method.

Also after every slight change in the air bleed screw, you MUST reset the high speed needle.

As you dial in the tuning, you'll see your reliable idle reduce. But don't determine your tuning condition by the idle speed.

Brad

One thing not mentioned in the above is how you broke in the engine. Did I understand correctly that you let it idle for a long time?

If so, that does not break in the engine. It should be set to run very rich at full throttle (this means breaking into 'four stroke' sounding ignition, then letting it run this way for about two minutes or so, then leaning it out to full speed for about 10 seconds, then running it back to idle. Repeat this for two or three full tanks of fuel.

Now, this may apply to ringed engines, I am not sure, but it is how I do all of my engines and they all run just fine. Do not hesitate to push that throttle to full open with a rich mixture. This will help seat everything properly.

The "pinch" method I am familiar with is running the engine up to full throttle, leaning out the mixture till maximum RPM, then quickly pinching the fuel line. If the engine trys to die, then go more rich, but ony about an eighth of a turn or so and pinch it again. When the engine RPM's increase slightly, then you are pretty much ready on the upper end. What you want is for the engine to change the note sound of the exhaust so that a perception of an increase in RPM is heard. After doing this, reduce the throttle to idle for a few seconds, then back to full and repeat until you are satisfied.

Follow BKDavy's instructions low end adjustment.

Well I started this thread a month ago and in the meantime took it out to the field. My instructor told me that there was no problem with the engine dying when vertical at idle. He adjusted the needle valve a bit, and we flew twice that day with no problems. It still does have the somewhat rough but reliable idle.

But as long as I have you're here: Yesterday I was working with a Magnum .46 that I bought used on a used trainer. The guy I got it from said it was a trusty good engine. This weekend was the first starting it since at least last year. I got the main needle adjusted to where it wouldn't die at full throttle when vertical, but at that setting, when I let it idle for about a minute and then punched it, it died immediately. Does your same advice apply that it's still too lean? This is a different engine mind you than the one we were talking about. Does it have an air-bleed carb? I haven't even touched the low speed idle adjustment yet.

Sounds like the low end is lean. I'm not sure if that has a low-end needle or an air bleed, but in either case, you need to richen the low end.

You can easily tell the difference - If it has a low-end needle, the adjustment screw will be inside the ring that has the throttle arm on it. If it's an air bleed, there will be a screw (Usually just forward of the throttle arm) and a small hole in the front, or top (forward of the main throat)

If it's a needle, open it in 1/8 turn increments.

If it's an air bleed, close it in 1/8 turn increments.

I helped a club member tune up his .46 AX last weekend on a profile Katana. The guy was having a heck of a time getting his engine to run reliably even though it was a used engine.

He had been monkeying with it far too much. I set it back to the recommended settings and started tuning from there.

He held it at idle for over 2 minutes nose up with a fairly slow idle ( 1800-1900 RPM ) . It held just fine.

Now that said, his fuel lines were pretty short, so I don't know how much this affected things. ( shorter tubes = less pressure required ).

But usually I try to shoot for a good idle nose up with about 1/2 to 1/3 of a tank, held for over 30 seconds and likewise nose down without cutting out. That is as long as the clunk is not uncovered.

Uniflow systems also help eliminate problems with the lower pressure at idle.


I'd shoot for a reliable idle nose up and down, which will help prevent deadsticks overall.

Well here's what happened tonight in the backyard: Got to a good high speed mixture with 45 degrees up, got a good reliable idle, smooth acceleration up to full throttle from idle. And the only issue was when I let it idle for a full minute or more, then gave throttle, still tended to die. Methinks in the air, this would not be an issue because you would never fly at idle for over a full minute, and this is the only problem I had. On the other hand, just wondering if it should be fully reliable at any throttle condition. I read the manual I found online for a Magnum
XLS, and it actually stated that after a long a idle a hesitatation or deadstick would be normal if you give it full thrust suddenly. This is actually an older Magnum GPA, not XLS, and I can't find a manual for it online, but I'm wondering if the principles are the same. This engine does not have the remote needle valve.

You might be a hair rich still, but don't mess with it any more. Fly the plane. You will find that on approach you might be idling for a minute or more, particularly with a trainer. One trick to avoid deadsticks on approach is to make sure you've had it at full throttle for a few seconds before you start your glide. This will keep the engine warm. Also, when you drop your throttle for the glide, raise it back up slightly. You can drop it back when you're just about on the field.

Brad

Likewise the engine tends to lean out in the air at idle in almost every other attitude.

As BKDavy said, you will not be flying it at idle nose up for very long.

I see very little here about tank location which would be important in the case of idle but not always full throttle . if its a long way to the tank or its very low that can affect the length of idle. also it is not always neccesary to adjust high speed after dealing with the low speed. .depends on how far out of adjustment & "sync" they are with each other. very seldom are they perfect anyway.as stated before SOME airbleeds have very little effect , other very noticeable . often depends on the mfr. 1/8 turn on some air bleed carbs ive seen had little or no overall effect. the airbleed carb is actually a rather simple crude affair compared to the two needle types.

Amen to that!

I hate the OS LA carbs in their lack of fine adjustability.