My training is going along quite well and my instructor is great, he's a very good pilot and is great at keeping me relaxed and teaching me to fly. He doesn't have a whole lot of experience at engine tuning though. I have a OS 46ax in my LT-40. After the first few break in tanks I took it out to the field and had one of the older guys with great tuning skills tune it for me. Its run good until the last 4-5 flights. (3/4 of a gallon through it now). The last few flights its been getting sluggish during the transition from idle to higher speed, especially if I throttle up too quick. Today I actually had my first deadstick. The thing that worries me is that the oil that was in the muffler today when I packed it up after the deadstick was not clear but a litle on the dark side. I packed it up at that point so I can take it out when one of the older, experienced engine guys is at the field.

I'm afraid it might have been too lean, does it sound like it may have been? What can I do next time to tell?

Sounds like the low-end is too rich. If it is "sluggish" when you advance the throttle it is rich if it just dies while idling it is lean- Go clockwise 1/8th of a turn at a time on the Low SPeed needle. (It is inside the throttle arm and you can usea small flathead screwdriver for that..)It is common for an engine with low time to needle the low speed reset once it starts to break in-- and a little dark oil is fine

Ideally you should be able to let it idle for 5 minutes (exagerration) 30 seconds is what I do- and when you advance the throttle quickly the engine should respond without being sluggish...

I remember when it was first tuned that it had a sluggish transition similar to now and the guy tuning it used the screwdriver to adjust the low end. As far as setting the high speed needle valve, what am I looking for? Am I looking for max rpm's then richen a click or 2?

Yep, always tune the high end first then fine tune the idle (low end) side. You have the right idea by getting max RPM on high then richen just a smidgen, because engines will tend to lean out during flight due to the increased air flow through the carb venturi. If it's nasty and sluggish on the low end, try to lean it out just a little. It won't take much at all.

I prefer the pinch test for setting the high speed needle.

At full throttle, briefly pinch the fuel line. If the engine sags and dies immediately, it's too lean. If it runs a while, then dies, it's too rich. If it picks up speed a little, then starts to die, it's right.

Dr.1

I've broken in and tuned a number of 46AXs in the last couple of months. A couple of observations for what they're worth............

Every one of them needed very slight leaning of the low speed needles after they'd been flown a couple of times. They've all been decent on transition right after breakin but started doing what you've experienced after they'd gotten a few flights on them. Each time, only 1/8 turn of the low speed was enough for then. None of them have taken that treatment more than twice.

When you get out to the field to fly next time, don't be chomping at the bit to adjust that low speed needle. Every time you start a new session, before you crank the engine, give the high speed needle a couple of clicks rich. You never want to start any engine too lean and that insures it. Then, after you've got the engine running, pull the igniter and let 'er run a short time to blow the muffler clean. Run her up to top rpm and right away turn the needle valve out until you hear her go rich. As soon as you hear that, start turning the needle back in until you get top rpm. You want to be positive NOT to be messing with the needle setting when too lean, and going out to rich insures that you start "safely rich".

When you've gotten top rpm, go a couple clicks richer. At that point you've got the engine cleared out so the next tests aren't screwed to begin with. And the engine is warm enough that "cold" won't screw the next tests either. How do you know when you're at top rpm? If you've come from a too rich needle setting, leaning has been raising rpm steadily. When the continued leaning finally starts to slow the engine, then you've found the top rpm. It's the rpm that was screaming at you just before you ran that needle in and the engine started to slow. Back the needle quickly to that top rpm, and then those couple of extra clicks.

OK....

Now take the throttle back to idle and adjust your throttle trim to your landing idle speed. Let it idle awhile. If it holds any idle for a minute tell yourself that whatever the next tests show, the lowspeed idle was close to being good and not to go wild with the screwdriver. Now, jam the throttle wide open.

Every 46AX I've had that then choked down took about 1/8 turn in on the lowspeed needle to run good.

If it didn't die when it stumbled, cut it off. If it did, kewl. Either case, give the lowspeed an 1/8th turn in and start it up again. Make sure you check the highspeed setting and that'll clear out the crankcase and muffler so the next test starts clean.

now... about the black residue..........

Every 46AX I've handled in the last couple of months.........

When they've got a good needle setting that is rich enough that they're not running too hot, their exhaust oil will show up on the airplane clear. If I've set the needle too lean, they've shown black oil on the airplane.

I would make the judgement from oil on the airplane after a flight. What the oil that's been left in the muffler looks like wouldn't mean a thing to me.

BTW, you're just learning right?

Then if you ever take off and the engine doesn't seem to be pulling and you see a lot of exhaust
OR the engine doesn't seem to be pulling and you don't see any exhaust
OR you don't like ANYTHING about the way the engine is running.........

You're learning to fly, right?
and you're learning to land, right?
and you need to practice landing........
so land the bloody sucker and reset that needle.
You'll get extra landing practice and that's good.
And you'll get extra needle setting practice and that's good too.

I use an old fashioned method. Set the high speed needle to max rpm, back off about 1 or 2 clicks. Then I get a buddy to pick up the plane. Holding it level I go to max throttle. Then my buddy tilts the nose of the plane up toward vertical. If the engine sags down, open up the high speed needle a click or two. Repeat. When I get the plane set where it doesn't sag down, I open the high speed needle another click. I work on the basis that engines running a shade rich have a long, long life span. Engines that are run lean don't have nearly as long a life and oftimes if set too lean will sag down and give you deadstick practice on take-off.

Once the high speed needle is set, follow the instructions in the above posts for setting the low speed needle.