Why does my engine keep quitting?
 

Hopefully somebody here can help me with this on going problem that has gone on for a long time with my O.S LA-40 for my Sig kadet LT-40 trainer airplane. What keeps happening is that my engine always sounds good during the run up on the ground, then when I take off, after about 2 minuets, the engine always quits and I have to make a forced landing in a glide. My airplane has been badly damaged because of the engine quitting when my plane was far away and I couldn't bring it back to my landing site. What usually happens is when I go to throttle up in the air, the engine just quits right away. Other times, I can hear the engine running rough all of the sudden then it just craps out. Can't find any apparent reason its doing this. Keep adjusting the mixture till it runs smooth and it seems to work on the ground but like I said, there's nothing more annoying then an engine that runs good until its in flight. The other day, my engine seemed unusually hot after it ran for a few minuets. Hotter than normal anyways. What could be the cause for this? I suspect some friction between the drive hub and the prop but I took apart the engine and found nothing. A lot of times after my engine quits, its hard to get it started again. And when I do run it up on the ground, a lot of times when I increase the throttle, the engine will want to conk out until I quickly reduce the throttle so that it wont. This is a very annoying problem I want to be fixed. I can never have any good flights without my engine giving me problems. I have wasted almost an hour last time I tried to get it started and keep it running. I have tried everything and can't figure what is causing all the engine failures. The engine is almost 3 years old. Do you think its wearing out?

Why does my engine keep quitting?
 

I am no expert but I have posted with similar problems and everyone has said that I was too lean!
First adjust the high speed needle for top RPM and then richen up about 3 - 4 clicks.
Then try the pinch test with the fuel line?
If you pinch the line for just a second and then release it.
If it dies right off it's too lean
If it speeds up just for a second and then returns to normal RPM that is "Perfect"
If nothing happens it is probably too rich.
The adjustment with the pinch test should be done to the low speed needle, and then readjust the high speed like before.
Have you checked for air leaks in the lines and tank?
Make sure your clunk is not flipped up front.
Please verify all of this with someone else because I have only been doing this stuff for about a month!

Why does my engine keep quitting?
 

Ditto to RCBOZO.

m_b

Why does my engine keep quitting?
 

I just printed this off another thread yesterday. I don't remember who posted originally and I do not take any credit for this info but it sure sounds like this may help you. So whoever posted this oridinally, thanks and all the credit is yours!

Here's a scenario: Pilot takes off, plane's engine sounds great. After several minutes of flying, engine seems to lose power, sounds kinda "thin", pilot keeps flying. Engine continues to sag, now full throttle is very weak, pilot now understands that maybe this isn't gonna clear up. Engine dies (what a shock! ), pilot calls for deadstick landing overshoots, tears off landing gear, etc. Never seen this at your field, right?

Here's the way that *I* set mixture on non-airbleed carbed engines (90% of the engines out there fit this category, but the theory is similar for air-bleed carbs). First of all, understand that the high speed needle has its main effect from 3/4 to full throttle, and the low speed needle controls everything from idle up to 3/4 throttle. It thus makes sense to me to spend the biggest majority of my tuning time adjusting the needle that controls the largest portion of engine running, right? Also, remember that there is a proper air to fuel ratio (mixture) that allows the engine to run properly. Too much fuel is rich, and too little fuel is lean. We "richen" the mixture by adding more fuel (turning the needle out, or counter-clockwise), and we "lean the mixture out" by decreasing the fuel (turning the needle valve in, or clockwise).

I start the engine give it full throttle, and lean it to it's highest rpm (peak), then richen it by maybe a quarter turn. Then with the glow plug igniter still attached, I slowly close the throttle to an idle rpm. At the lowest rpm that the engine will still reliably run, I then remove the glow igniter. If the engine dies immediately, I know it's too rich, and I then lean out the LOW SPEED NEEDLE by 1/8th of a turn (don't touch the high speed needle). Start the engine again, (and this is important) give FULL throttle briefly to clear out excess fuel, then slowly close the throttle again. Remove the glow igniter, and this time it may run a little longer before it dies, so lean the low speed another 1/8th turn. Re-fire the engine, give a burst of full throttle to clear it out, and slowly close the throttle again. remove the glow igniter and now notice that the rpm DROPPED a bit when you removed the glow igniter, but the engine kept running. We're getting there. It's still too rich, and you'll prove that by opening up the throttle and hearing the engine "blubber" then die. That's because excess fuel has collected in the crankcase during the rich idle, and when you opened up the throttle, the excess was pulled into the cylinder, making it WAY too rich. Supposed you were on a landing approach, and decided to go around, you throttle up but the engine "blubbers" and then dies (another thing we haven't seen, right?). Yep, the LOW SPEED needle was still too rich, allowing excess fuel to collect in the crankcase, just WAITING on you to try to go around so it could "LOAD UP", blubber, and die!

Keep leaning the low speed needle down until it idles well, but now, when you open up the throttle, it HESITATES instead of BLUBBERS. When this happens, you've lean it down too far, so richen it up 1/16th of a turn and try again. You know you've got the LOW SPEED needle right when you can fire it up, remove the the glow igniter, and the rpm doesn't change AT ALL, and you can open the throttle up, and it doesn't blubber or hesitate, it just runs!

The final thing you do is re-adjust the HIGH SPEED NEEDLE, leaning it to it's highest rpm (peak) and then richening it up maybe 1/8th turn to give it a slightly rich mixture. We also know that the fuel mixture will change in flight when you point the nose up (harder for fuel to travel uphill) and also as the fuel level in the tank changes. In both cases, a leaner mixture results, so we actually need to set the mixture a bit further on the rich side to account for this. While the engine is running at full throttle, CAREFULLY pick the model up and raise the nose to at least a 45 degree angle while listening to the engine. If the engine sags a bit, then you'll need to richen up the high speed needle 1/16th turn. Try it again, and when you can point the nose up and the engine doesn't sag, but maybe shows a slight GAIN in rpm, you know you've got it right.

Now the engine will be happy, and chances are will reward you with reliable running. If you've got one of the few engines with an air bleed adjustment for low speed adjustment, the theory is the same, just refer to your manual to see how to richen and lean the low speed mixture.

Why does my engine keep quitting?
 

Thanks everybody for your help. When I get a chance, I'm going to try all of these. The problem is, is that my mixture knob seems really sensitive. I move it one click and it makes a huge difference. One time, all I had to do to stop the engine from running was move the mixture knob just one click. If I try to half turn it or even a quarter, I can just see my engine just quitting all the time, but I will give it a good try.

So that's what causes the engine to just die when you increase the throttle? Excess fuel in the crankcase making the mixture too rich in the idle? I finally know why that happens because that has been my most common problem. And to fix it, you need to lean the mixture? My problem is knowing how much to lean or enrichen it by. I either do too much or not enough because my engine screws with my mind. And yes, I do the thing where you hold your airplane up at a 45 degree angle to listen for the increase in RPM. Somebody told me that if you hear the increase in RPM, you know you have the right mixture setting. I did that, heard the increase, took off and the engine still quit. Man I hate that. These engines are so deceptive.

Why does my engine keep quitting?
 

Sounds like you may have some trash stuck in the needle valve, or you have too much fuel pressure for some reason.

Why does my engine keep quitting?
 

OS LA engines have airbleed carburetors. The adjustment of the low speed is very similar, except you turn the airbleed screw in the OPPOSITE direction you would turn a low speed mixture screw.

Airbleed carburetors control the idle mixture by regulating the amount of air that enters through that tiny hole in the front of the carburetor. The screw on the right side of the carbuertor is what controls the size of the opening.

Let the plane idle for a good 10-count, then quickly firewall the throttle. If the engine dies or hesitates, turn the airbleed screw IN 1/4 of a turn. If the engine blubbers and smokes, turn the airbleed screw OUT 1/4 of a turn. Airbleed screws are much less sensitive to adjustments than idle mixture screws, so you need to move them more to see any results.

While you may not get an airbleed carburetor to ever transition perfectly, you should be able to get a reasonable transition out of it. If you find that you have completely turned the airbleed screw out of the airbleed hole, and the plane still blubbers when you shove the throttle ahead, disassemble the carburetor and drill out the airbleed hole with the next size larger numbered drill bit. 1/64" or 1/32" of an inch may be too much, which is why you need the numbered drill bits.

Why does my engine keep quitting?
 

Its his bleed air hole, it needs to be drilled out one size more so it doesn't load up at idle. Common prob with the LA .40

Overly Sensitive Needle?
 

Were you speaking of the full-throttle condition? What prop are you running? The reason I ask is that an overpropped engine will be extremely sensitive to tiny needle adjustments, at full throttle.

My Tower 40's like a 10 X 7 APC, but some of the fellows tell a lower pitch would be better. Mine run fine, and idle better now that I've drilled out the idle air bleed hole by one drill bit number.

Good luck,
Dave Olson

Why does my engine keep quitting?
 

One of the problems here of course is that of a relative newbie not wanting to spend big bucks on an engine that will most likely get trashed. This exact thing happened to me :mad: . I had an O.S. .40 with that $#@&*^% airbleed carb and essentially couldn't complete a flight. I finally gave up and bought a Super Tigre .40 and soloed in about a week. I'm not familiar with the new generation of O.S. bushed, single needle, lapped piston engines but it sounds like not much has changed. This won't solve your problem, but I think you need a better engine!

Why does my engine keep quitting?
 

Hi!
It sounds as if you run your engine too lean! Just open the highspeedneedle somewhat and try again!
But........Here is what recommend for you OS LA .40.
First ..you dont have to use more nitro than 5% to have this engine perform at its best! 15% nitro is max!
The propeller is vital....use a 11x6 APC for relaxed and slowflights with good climbing power (if you fly at sea-level).
A 10x6 will produce more explosive power and this is not recommended for a newcomer...
Fuel...well I use 15% syntetic oil like most people in Europe...but "good ole" 20% castor oil will work too.
Fueltank size is important ...a 240cc (8oz) is perfexct for your engineand every other .40 engine.. see too that you have the tank well surounded by lots of foam padding and that the tank is placed with the center line inline with the carb orifice when the airplane is hold horizontal....or 1cm below the centerline! This is very important!
Naturally you use pressure from the silencer to the tank!
A good glowplug to use is the OS 8 or the Enya 3.
And do not use sheap plastic spinners!
If you are going to use a spinner use a Tru Turn aluminum spinner! I myself prefere aluminum spinner nuts on my sport airplanes , easier to start engines that way .....only turn the spinner cone on the starter inside-out!
Setting an engine is something you have to learn...the pinch test might work ...but I dont use it ...A better way to set any engine is by ear....you listen to how the engine sounds and take appropriate action....
Your OS LA .40 has an airbleed carb which will work as good as any other two-needle carb...and it doesn't have to be modified at all to function perfect! Just listen to how the engine sounds and act accordingly...allways setting the highspeed a tad rich when holding the nose of the plane straight up! This is the test you should do every time you fly your airplane!

Good luck!
Jan Karlsson
Sweden