Flight Risk here with an update. I rechecked all hoses and needle valve and carb for leaks. I drained the crankcase from all the old oily fuel. Mounted the engine on a test stand and ran a few ounces of fresh 10% nitro, 20% oil through it. It ran great as new. Mounted it on the plane and filled the tank with the fresh fuel. It started and ran great for about 5 minutes then quit suddenly as usual. I opened the throttle and looked into the carb and the fuel was percolating. I drained out what fuel i could and spent several minutes trying to start it again. It would run 5-10 sec. and quit. Seems like it is drawing in fuel faster than it can burn it and the rest is building up in the crankcase and percolating out the fuel to leave the oil. I have tried leaning out the engine as far as I can without dying. I've tried several plugs. Evidently the fuel isn't the problem. I guess I could try a hotter plug (i've used an A3, A5 and Fox Miracle plug) or try to find fuel with 10-15% oil. Back to the drawing board.

FR

flight risk....yoiu say the fuel is percolating (boiling?) when the engine stopped. That indicates to me that the crankcase housing around the crankshaft is overheating (and possibly the rest of the engine as well). A plain bearing engine like the LA needs a minimum of 20% oil and strictly speaking all or most should be castor. Most RC fuels have 18% oil but a couple are actually only about 16% because of the way they mix it. Get a good brand of fuel that clearly says on the label just what's in it and how much, then maybe add a bit of castor to be on the safe side (22% oil is ideal).

Spaceclam...an engine will idle perfectly well without muffler pressure because that's what they all really do. Soon as you come back to idle there's almost no restriction to the exhaust and whatever pressure was in the tank then bleeds back through the pressure line into the muffler. They'll all also run perfectly well at full throttle without muffler pressure too but you'd have to open the needle considerably and then it'd be very sensitive to pointing the nose up so it can really only be done on a test stand.

that's wshat i have been saying the hole time. iot is probably overheating.

That is likely your problem, and is the fastest way to ruin an engine. Richen it up. The reason it dies after 5 minutes is that you're running it too lean and it overheats. I see folks at the field do this nearly every day I fly, and they swear up and down at their engine when in fact they're just not running it as they should be.

Do you have any experienced help available? Glow engines take some getting used to.

MikeL,
I agree completely. FR, everything you've said so far leads me to believe that you're running that engine WAY too lean.

AllThumbs,
Turning that needle valve 1/4 turn is too much when adjusting. One or two "clicks" at a time.

Are you saying that you're needle valve is only open 1/4 to 1/2 turn from closed while running? Something just ain't right there.
Dennis-

- which you've no doubt seen and know already (so no revelations here).

Yes, three quarters of a turn open sounds like a whole lot, and very rich compared to what you guys are used to running.
But the OS manual has a diagram w/steps (or needle valve positions) numbered 1. thru 7.

It shows a "rich" needle setting for starting the engine at position number 1).
1.)that is almost 360 degrees for open - or a full turn (from the closed position, which is what I called a 3:00 O'clock position).
2.)begin "leaning" with a clockwise turn of the needle to a point that looks like a 75% or 3/4 turn from the closed (or 3:00 O'clock) position at which the
3.) ....the exhaust note changes.
4.)dissconnect glow starter
5.)advance clockwise (until you hear an intermittent 2 stroke note superimposed on low 4 stroke sound at a point that looks like a half turn open at 9:00 o'lock - from the 3:00 O'clock closed position.
6.)clockwise turn from this point gets a clear high pitched 2 stroke exhaust note, with a practical best optimum needle setting w/in a 20 to 45 degree setting around the 12:00 O'clock position


Anything leaner than that last needle setting is called "maximum rpm setting" - or "Lean".

So, I agree w/you, - I'm obviously running a pretty rich needle setting at a 3/4 of a full 360 degree neeedle turn, BUT that's what the manual says to do.

In fact, it says to do the first three or four flights this way at the 3/4 or 75% neeedle setting in number 2.)above....where the sound breaks into 2 stroke from 4 stroke.

I'd like to "lean it up" for more rpm - but it wouldn't stay running after I advanced the throttle past 1/3 power.

I don't think I want to do dead sticks w/ the instructor for the first three or four flights, which (based on my ground tests) is likely to happen if I set the needle any leaner than 3/4.

The manual says after ten to fifteen flights, the engine should run continously at optimum setting w/o loss of power.

I'm concerned that based on what some of you say, the ABC type engines should be "broken in" hotter (leaner) than ring engines - so I'm not sure how long I should be running it rich like this.

is your fuel tank mounted in foam? if not it could be foaming up from the vibration of the engine! just a thought.............

True. I made that mistake because the manual said to do it on my first plane. It said that on my second plane, but by then i knew better than to take them seriously. I switched to a different company, and they said the same thing. I think every kit says to do that, but it will only cause problems. The 46 fx is not ringed. The break in instructions are different for a non ringed engine than for a ringed one.

does that carb have 2 needles? sounds like the low end one is lean which makes it lean on transition

AllThumbs....I've looked at that needle setting chart on the OS web site (not owning an OS) and it's very confusing. It's not actually based on the needle being fully closed (because then your engine won't run at all) but it's based on whatever needle opening you need for proper operation. For instance, the maximum lean (or peak) setting at the 3 o'clock position could mean that the needle was open 1 1/2 or 2 turns from fully closed. All the other positions are just a general guide as to where the needle should be to get a certain mixture. BTW, they're also assuming you'll put a file mark on the needle end so you can see how far you turn it. What I do is close the needle (gently) then mark it at the top or 12 o'clock position. Then you can see exactly when you've opened it 1 turn, 2 turns and so on.

The number of turns the needle is opened is going to vary depending on what type of fuel you use (mainly) and most engines need about 2 turns or more to be certain they won't run lean, especially on the critical first start of a new engine where you have no idea how it's going to run. The only setting that's instantly recogniseable is where the sound changes from a 4 stroke (deep growl) to a 2 stroke (higher pitched clean sound). That's the equivalent of what they call the 9 o'clock position but the needle itself could be open maybe 2 1/2 turns from fully closed.

The OS diagram simply means that full lean will be about another half turn closed from that point (once again, more or less depending on your fuel).

Sorry to be hogging this thread, I should 've started a new thread before running away with this one.

a.)Yes, I have some thick 1/2 inch foam rubber-banded around the tank, open at the top.

b.)Nope, one needle valve on the port side of the carb, and a long upright screw in a spring on the starboard side.
Haven't fooled with that one yet...I let my instructor adjust that the last time I was at the field.
I'll be talking to him again - hopefully tomorrow afternooon.

Downunder, Thanks for pointing out the "relative" position of the settings...which I take is variable, based on the known benchmark, which is the breakpoint from 4 stroke to 2 stroke.

If what you said is true...... <<"The number of turns the needle is opened is going to vary depending on what type of fuel you use -mainly- and most engines need about 2 turns or more to be certain they won't run lean, especially on the critical first start of a new engine">>....then maybe I'm still in a slightly lean setting (instead of overly rich setting) afterall, which gives me a piece of mind according to the current philosophy of breaking in an ABC engine hotter.


I'm turning this "problem" over to my instructor
- he flys YS four strokes these days but he no doubt had to go through the 2 stroke portal to get where he is today.
He's got a good ear too.

that wouldn't explain the cut-off-in-5-minutes problem. only overheating would.

AllThumbs...yes, I think you're running far too lean which is much worse on any engine than being too rich. Chances are that as the tank level gets lower in flight the engine continues to lean out until it's at a point where it's too hot to run anymore.

You have probably trashed the engine by now. Runnning a 2 stroke lean is REALLY bad for it, not to mention freezing up or repeating it. If your engine still runs, It will never produce the power it could have or last nearly as long. I would invest in a new piston and sleeve, and break it in again.