Hi guys, i wanted to go fly yesterday, it was a nice day here in quebec.... about 30 degrees. Got to the point of starting my engine....

filled the gas tank, closed up my needle valve totally and opened it like the os book says (1 1/2 to 2 turn countercolck wise). I did 2 turns. Hooked on my glow heater and started it...

At mid range of throttle i was disconnecting my glow driver, then full throttle for needle fine tuning adjustment. I had to close it up for uptimum engine setting... then i opend it up about 1/8 richer (i heard that it's good to do that, because the air in altitude is a bit more denser that at the ground level). Engine was reving fine .... from full throttle to idle ... with a good response..

At that point i was walking behind my plane while it was taxi-ing just before take of... well were is what happend... not even a minute after it was taxi-ing... at about 1/8 of throttle not even... has soon that i was applying just a bit of throttle for take off the engine died right away.

got the plane back to my stuf... retried... and same thing again...

I thought that i could have been of my glow plug, i had some spares... replaced it with a fresh one. But same thing occured...

Well, yesterday.... i spent about 2hours... just to try to get my plane to get to take off but without success!!![:@]


Now please.... please help me out....

I thought that it could maybe be my gas.... i am using the same gallon of gas that i used this summer... it's 15% nitro but there is really not much in there... could it be the gas that is not good anymore??

What else am i not understanding wight here??

have a nice one.

Marc-Andre

Yes it could be the fuel...Do you close the needle valve and reopen before every flight day? There is no need to do that...I'm guessing you now have an air leak at the needle valve,,,,,replace the o ring and see what happens....

no, it's because the last time i used it was summer time here.It's winter now and i had to adjust the valve from scratch. And i never closed it tight before, i will change gas...and try again.

When a warmed up engine that has a recently adjusted high-speed needle dies on application of throttle, one of two things is happening. OK, maybe your glow plug is also crapping out on you, but after checking that...... You've probably got a low-speed needle that needs adjusting.

If the OS46ax is fairly new, there is a good possibility that the low-speed needle needs a small adjustment.

Best way to do that is with the pinch test. It's described in detail in a number of threads around here. But the sound byte description is that you pinch the fuel line closed while the engine is idling and adjust depending on what the engine does when it runs out of fuel.

Let me make a suggestion about setting your needle first thing each outing.

Most experienced modelers don't close it completely and start over from a mfg suggested opening. It's not just laziness. It's actually more reliable to start an engine with it's last needle setting. Only thing that throws a monkey wrench into that is if the engine hasn't been run since the season has changed. And that's not hard to deal with if you're just slightly experienced.

What you do is think about how the temps have changed since last time you ran the engine. If it's gotten colder, open the needle a bit. If it's gotten warmer, close it a bit. And it'll start more reliably than some mfg's setting because you've found a good setting before for your altitude and climate where you fly. But no matter if you give it a click or two the next is important no matter what.

Once the engine is running, it's always a good idea to open the needle to insure a safely rich setting. How to do that? Open it a couple of clicks (keep in mind how many) and if it speeds up as you richen it up, keep opening it up. You want to make sure the needle is opened until the mixture shows rich. Until it does, the setting isn't safe. When it does show rich, start back. You've insured that your needle adjustment is starting from rich. Now as you start to close the needle and the engine speeds up, you're heading for the optimum setting from a guaranteed safe adjustment.

Bring the needle to where the engine has reached peak and just starts to slow down. You don't know it's at peak until you've leaned it past peak and you discover that by it slowing down. Then open the needle back up a couple of clicks to where it was at your newly discovered peak. And then open it more. How much more?

Pick a number like 3 clicks and test fly. If it seems too lean then land and give it a couple more and test fly again. One outing and you'll know what to do next time. And you've added a check mark to the list of things that measure your "experience" rating.

So you still want to know how to do the pinch test?

It's fairly simple. If you pinch the fuel off and the engine speeds up just before it runs out of fuel, the engine was too rich. If you do the pinch test to an idling engine, then the lowspeed needle is too rich. You can do the test with the throttle wide opened and it'll tell you how the highspeed is set. But thats easier to do with "experience" (what you just picked up in the post above). If you pinch off at idle and the engine just stops, the lowspeed is probably too lean. Simple?

When an airplane engine dies on throttle up, it's usually one of two things. Weak plug or bad lowspeed needle setting. It's usually the lowspeed or idle needle setting. And it usually happens with new engines that're just then breaking in.

BTW, right after getting an engine started you want to let it warm up and you want to clear out any excess fuel from the starting process.

We often do things starting that put raw fuel in the crankcase. And lots of people start their engines at half or less throttle. No matter, if the engine starts, let it run at low to medium speed while you move stuff out of the way.

I usually start with 3 clicks on the throttle from throttle stick closed. And when they start I let 'em run that speed while removing the igniter and such. And I listen all the while. And about the time I get 'em out of the hold down, they pickup speed a bit. I've always believed that pickup is the excess clearing at about the same time they've warmed up enough. I give them a steady throttle up and listen. And I look at the exhaust for some visible. After you've done it a couple of times you know what you want to hear and what you want to see. Depending on the weather the needle may take a click one way or the other.

The engine is then cleared out and warm, and needle probably set ok. I bring it to idle and let it run some at idle. Now it can be checked to see if it'll take a quick throttle up. If not.......... pinch the sucker. If you try to test before you've gotten the primary needle set at least close, and before the starting fuel is cleaned out, and before the engine has had a bit of flatout run, it'll drive you crazy.

And we don't need anymore crazy modelers.......

well, that the hole point.. yesterday, at one point i was really getting frustrated. But this is a hobby, a passion. I dont want to be out there and be all pissed off because this little tricky engine is playing with me. I was really hoping to have the plane take off but not even. Hahahah, now i laugh of it..

I just need to gain some experience, learn from other, like you that took the time to help me out.

BTW where is the low speed setting located on my engine?

This afternoon, i'll take the plane out for some more engine test. And try to start from rich to lean... makes sens too.

again, thank you.

Marc-André

It could also be the glow plug. Swap that out and see what happens.

CGr.

One other thing...

Check to see that the muffler nipple is unobstructed.

I've had this happen on occasion, and end up trying to find a problem that really doesn't exist.

The lack of pressure will end up throwing off the engine tuning and causing run-up problems.

it's not the glow plug because i replaced it but with no good results. I will also verify the muffler nipple for obstruction.

thanks


Marc-André

On the OS46AX, the low speed needle is hidden away and very hard to find. It also requires a very small screw driver to adjust it. The carburetor throttling is done with a barrel that your throttle pushrod moves. The barrel has an arm the pushrod connects to. If you look at that arm you will see a hole in the center of it's base, the part that rotates with the throttle barrel. Look closely and you will see a screw down inside that hole. O.S. calls the slowspeed needle, the Mixture Control Screw. All you can see in the hole is the head of that screw.

It takes a very small screwdriver to fit in that hole. You adjust the screw with the engine stopped. The process is also described in the OS users manual on page 23. Unfortunately, they don't provide a picture.

It does sound like a rich idle is loading up the engine from extended low speed running. When you adjust the idle mixture do NOT crank it shut and start over like you did the high speed needle. The idle mix is VERY sensitive and should be done in 1/8 turn increments to avoid going too far. OS routinely sets the idle mix rich on new engines to avoid lean runs that will damage the engine.

Stop the engine for tuning to keep your hand out of the prop.

marcus028
FYI
I have an OS 46 AXi on my Nexstar. When it was just getting broken in, mine did the exact same thing yours is doing. I read somewhere on here in a previous post to do the pinch test, just like da Rock is telling you. Just be patient, take your time, and you will get it. I did have to go buy a set (I can't buy one of anything!) of small screwdrivers from my LHS to make the adjustments, but my engine has been running perfect (knock on wood) ever since, and I'll bet yours will too. Keep asking questions, these guys are great at helping others.
Pete

In the Winter season I change the plug from an A8 to a A3. It makes a difference!

Sounds to me like the low speed needle valve is off a bit. You can check this before you even start to taxi by idlying the engine for say 30 seconds and then hit the throttle. If it starts to smoke and sputter in stead of speeding up, the low speed valve is set too rich. If it dies right away, its too lean. Make small adjustments, 1/8 of a turn at a time and get smaller as you get close. Once you have it, you should be able to idle for a full minute, or more, hit the throttle and have instant high speed throttle repose.