Engine Problems!!!!
 

Hey guys,
I just flew my avistar again and there seems to be a big problem with the engine, i always fly for about 5 min and then the motor is going slower and the motor is going up and down (slow and fast) for 20 seconds and then it just quits, my tank is about 3/4 full and I had the problem on all my flghts today (Always made a nice dead stick landing)
Where could the problem be? I checked the tank yesterday and everythink semmend fine! Mabe the needle value?

-Nik

Engine Problems!!!!
 

It sure sounds to me like you have one of two problems. Either you have something obstructing the fuel intake ... clogged filter, or gunk in the carb, or there is some type of air leak in there. Double or triple check all of your connections, make sure your filters are all clean, make sure there are no pin holes in any lines.

I have an Irvine .40 that drove me crazy with this type of problem and I found that there was an air leak between the carb and the manifold. Some high temp RTV sealant around the carb and all problems cleared up.

You may have more help if you give the details of the engine.

Just my 2 cents ... Bo

Engine Problems!!!!
 

Air leaks in the fuel system, or around the needle valve are good possibilities. I'd also make sure that you're not running it too lean.
Dennis-

Engine Problems!!!!
 

Well if it there are leaks in the fuel system why does it run for 5 min without any problems? Also how can i make sure the engine is not too lean?

-Nik

Engine Problems!!!!
 

Try the obvious, and just open up the needle valve a few clicks and see if the problem goes away.

If that doesn't work, it could be an air leak inside the tank, in the clunk line. When the tank is full, the engire clunk line is in the fuel, but as the fuel level drops, the leak is now exposed to air and sucks in bubbles. Depending on the tank, this can eaisly happen where the clunk line attaches to the tubing that goes though the stopper.

Also check to make sure the clunk is not stuck against the front of the tank.

Make sure you don't have the fuel lines reversed. Usually you get shorter than 5min flights that way, but it's worth checking.

Easiest way to check is to see if you can pump the tank empty. If you can't empty the tank with your fuel pump, then you know you have a problem.

It could also be fuel foaming.

Next time it happens, take the plane back to the pits, and re-start the engine with out adding more fuel to the tank. Take a close look at the fuel line. Do you see air bubbles? Pick up the plane, and hold it nose up. Does the engine keep running with either a slight RPM increase or no change? If you notice the RPM drop off, or the engine quits, you are too lean on the needle or have some other fuel draw problem such as the ones above. Usually it's too lean on the needle valve.

Engine Problems!!!!
 

Two easy tests to check an engine to see if it's too lean.

Both are best done with the tank 1/2 full of fuel, though they work ok with a full tank as well.

Both are done with the engine running at full throttle.

First, pinch the fuel line briefly with your fingers or a clamp. You should hear (or observe with a tach, but I do it by ear most times) a slight RPM increase. No increase means you are right on the edge, best back off a click or 3. An RPM decrease means you are too lean. Of course, if you hold the pinch long enough, the engine will drop off and die as you cut off the fuel. But you should still hear an RPM increase before it drops off.

Second, lift the airplane and hold it vertically nose up for several seconds. Again, you should hear a slight RPM increase. Any drop in RPM means you are too lean.

Some guys who have 3 hands do both, hold the airplane vertically, then do a pinch.

Engine Problems!!!!
 

How much foam do you have wrapped around the fuel tank, and is this foam still uncompressed? An/or how well-balanced is your prop?

I'm thinking along the lines of fuel foaming.

Engine Problems!!!!
 

It is probably overheating because there is some obstruction in the muffler, or the muffler itself is too restrictive. The other possibility is of course, too lean. What happens is it will run erratically and then finally freeze up. Try running it at a lover throttle setting, with the needle valve opened up a couple of clicks. Tell me what happens

Engine Problems!!!!
 

Allright guys thanks for the help!
Now i have one more question: When you go under the RTF Avistar accesories page they say you need a preciosion filter: http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXK134
Do i really need it? (It doesn't say anything in the manual) Also where should i put it?

-Nik

Engine Problems!!!!
 

That filter just goes between the tank and the carb. I don't use them. I didn't catch what engine you are running. I have a couple OS engines that are doing what you are describing and it seems to be the needle valve leaking. I wish they would put them back in the carb where they belong. I am almost to the point of selling them and getting a different brand. A few more tests will tell. I took off my fueler and will see if maybe that is the problem. I am hoping it is. I have the same problem on 3 planes. What a pain.

Engine Problems!!!!
 

i got a os .40 la

Engine Problems!!!!
 

Ok i think i could fix my problem with installing a fuel filter but where should i install it? At line 1 or 2? (See Picture)

Engine Problems!!!!
 

Put it in Line 1 so it's before the needle valve. This is what you must protect against getting any dirt in. The opening is so fine that the smallest speck can badly affect the mixture making it go lean. Lean is what kills an engine.

Engine Problems!!!!
 

I rather doubt this has anything to do with particles in your fuel. It's either too lean (my guess) or an air leak in the tank.

Engine Problems!!!!
 

Check presure line from muffler to tank.

Engine Problems!!!!
 

My guess is fuel foaming. While the Avistar is a great plane, the inherent design flaw is the fuel tank. It is mounted directly attached to the firewall and very prone to vibrations thus causing the foaming.

Make sure your prop is balanced as perfectly as you can get it since an unbalanced prop will cause the most vibration. If that does not work you my have to make some modifications. If you pull the tank out of the hole in the firewall you will have to seal that hole up somehow to keep fuel from leaking inside. Wrap the tank in foam and secure it.

Good Luck!

Engine Problems!!!!
 

of two os engines are doing that, you aredoing something wrong. Os engines are ONE of the best names in miniature glow engines. As i have stated in other threads, i have not had much luck with the la series, but i am 100% impressed with their four strokes, and their higher-end engines such as the fx, sx, and i have heard only miracles about their fuel injected engines aswell.

Engine Problems!!!!
 

How do you fix a needle valve leak? my Os46 Fx has the same problem. Runs fine for 2-3 mins and then quits. Checked for all leaks,pinch test, foaming etc. I am suspecting it is a needle valve leak. The problem is that engine reaches peak rpm when the main needle valve is open only half turn from fully closed. It does all sorts of fluctuating and coughing and then quits. I'll never buy a Os engine again.

Engine Problems!!!!
 

As spaceclam said the higher end engines are great, but like NIK I also have an os 46la that does the same thing, I have plenty of experience with smaal engines, I set it, fly it & it will run great for 2-3 minutes. Then it will start slowing down, loosing power until it is a dead stik. I have tightened all the engine screws thinking I had crankcase pressure leaking or head leaking, made sure the carb was sealed good to the crank case. This engine has maybe 20 flights on it & I have tried every thing I can think of to make it run right to no avail. It ran good for about 12 flights & has been nothing but trouble since. I have quit trying & wrote it off as junk!!
Any Ideas???
Gil

Engine Problems!!!!
 

I've got the same problem with a 40LA, I was told it could be dust inside the cylinder as well, my be worth to check that as well.... I started haveing this problem after a crash so I'll take it appart and try all the advices in this thread as well

Engine Problems!!!!
 

I have the same problem with a K&B .61, and it's fuel foaming in my case. Plenty pressure from the muffler combined with an RTV-mounted tank. I'm going to try adding a few drops of Armor All.

Engine Problems!!!!
 

Try this:
Get the engine started on the ground, and set the needle right at peak. Then push the needle in varous directions, but don't turn it. If you hear RPM changes, the o-ring isn't sealing. Put a bit of fuel tubing over the needle to help seal out the air. It's a "standard" thing I do to my Magnum engines to fix mixture funnies. OS engines usually don't need this, but it can't hurt.

When the engine is running, do you see air bubbles in the line before the needle valve or between the remote needle and the carb?

You might have an air leak in the carb. When you installed the carb, did you really push down on the carb as much as possible before tigtening up the screws? You really want to compress that o-ring.

Engine Problems!!!!
 

a leak, or crud, thats my guess. I always fly with a filter, but you have to be careful with them also, cheapy filters can develop leaks. I like the types where I can screw them together real tight. I even have a filter in my bottle as I draw fuel out of it and into my tank. Double filtered before it even gets to the needle valve. Be very careful with your fuel bottle. Don't leave it open for extended periods and don't let dirt like grass particles get into it. Leaks can be anywhere, check all fuel lines, and bolts on the motor. If you have a loose backplate or head, you're definitely going to have those problems listed. Sometimes the best thing you can do is take motor out and put it on a test stand and just start eliminating problems, one by one. Frustrating as hell, but it should run correctly.

Engine Problems!!!!
 

You know these are all good suggestions ,!!!!!!

but the most obvious has been left out , send the engine back to os and tell them to make it right or replace it .


I will work only so long to make one run as it should then it becomes a manufacturer problem.

Highlander

Engine Problems!!!!
 

Highlander,
Well, that's not a bad approach if you've really had several guys who know engines look at it personally. The best way to "fix" a problem engine is to get a local engine gruru to go over it in person and make it work.

Oh, here's a good one I just remembered. One of my students had an OS .46FX, and it was cutting out whenever we went to full throttle. Not always, but most of the time. He had a K&B glowplug in it (1L or HP, not sure which). One of the local guys (not me) suggested replaceing it with an OS #8. I figured there was no way it was the cause of the abrupt quitting, but we tried it anyway. What do you know, fixed it right up. Now, I run K&B plugs in all my engines, including OS .25FXs, with no trouble. And I run mini-pipes (mousse cans) and 15% fuel.

We pulled an OS #8, and a K&B 1L and held them side by side. They are both listed as "Long" plugs, but wouldn't you know it, the K&B is noticeably longer than the OS. (Ill avoid any jokes about who's definition of "long" means what here)

Apparently that was driving up the compression and causing all kinds of troble. If we had tried two or 3 glow plug gaskets, I'm sure it would have fixed it as well. Or if the engine had been a bit older, when the compression isn't quite as high, I bet it would work fine. The smaller engines usually like a higher compression anyway, so that's why it doesn't bother the .25FXs that I have.

I don't think this is the problem in this specific case, but you never know.

Engine Problems!!!!
 

For some reason both OS and Enya plugs are an inbetween length. The extra length of a normal "long" plug makes very little difference to the compression but does put the coil slightly closer to the piston. This can have a slight affect on the ignition point but it's probably not noticeable. There's an optimum ratio (which I can't remember now) between the bore size and the distance of the plug away from the piston at TDC that's about 5:1.

Engine Problems!!!!
 

I think the loosing rpm thing is overheating. As it heats up to it's maximum opperating tempurature, the piston has a tendancy to expand faster than the sleeve, which is why it will freeze up. Because the la series is not ringed, i think the drop in rpm is due to the tightening fit between the piston and the sleeve, which adds even more heat to an overheating engine. If the engine is cowled, you may want to consider increasing the cooling effect and see what happens. Also, if you are using an aftermarket muffler, it may be slightly too restrictive for that particular engine. Two strokes need enough backpressure to equelize to a certain degree the pressure behind the piston with the pressure on top of it. If there is too much, It will have a hard time expelling hot gasses, causing it to overheat in muinets and die. It can't hurt to check it out. Dust inside the cylendar would have trashed it by now, and it would either run like crap or not run at all. If there was dust inside the cylendar, It would have been ground between the piston and the sleeve, scarring the metal, increasing blow by, and greatly decreasing the engine's life. Unless you put dust in there, there is no way it could have gotten in there.

Engine Problems!!!!
 

I went out with my 91 FX last night and did some more testing. The 46 FX does the same thing. Both do as you are saying. The conclusion is that the remote needle is leaking somewhere. There is no air in the main fuel line, no bubbling in the tank, and a ton of air in the line from the needle to the carb. Every engine I have run with the remote needle has this problem. I have a letter in to the manager at hobbico about it and will let you know what I find out. I am really close to the end of my patients with these engines. I have a lot of them and they all do it. Really close to dumping all of them and going to a different brand. Hate to do that but man is it frusterating. We will see what OS says. My next step is to put a different engine on the plane and not change the fuel system and see what happens. I put the engine on a different plane with a new fuel system and the problem moved with it so I know it is the engine. The remote needle is a pain in the butt and I won't buy another engine with one.

Anyone know of a good carb that fits the 91FX with no remote needle?

Engine Problems!!!!
 

You shouldn't be having problems with the remote needle, but I'd admit, its one reason why I don't have any engines with that feature. Have you tried replacing the rubber washer in it (not sure if it has one)? Or slipping a piece of large tubing over it to seal it? Have you tried backflushig it to see if there are any trapped particles? In controline we'd always backflush the needle valve assembly when we had those kinds of problems. I wouldn't give up on OS, they are top notch motors. I'm running Thunder Tigers.

Engine Problems!!!!
 

Montague

The approach is one of simplicity, Ive paid the money to have a 1 or 2 year warranty . on the new engines that I buy.

This warranty is offered by the manufacturer and I believe this is based upon their experiance that sometimes an engine will get through their quality control that simply is not right ,

and in some instances never will be !!!!!!

Ive found most of the producers of these engines ,and I run several brands, to be really quite fair and willing to make the customer happy.

I run OS, magnum, and supertigre and have a stock of both new and used engines ,

any engine that will not tune readily and hold, I send in , Ive had some replaced and some where just parts were replaced but in the long run the simple fact is if your having engine problems your plane is grounded ,or should be !!!!!!

I run all of my engines on the test stand before I install them in a plane , if they wont perform there, then they never see an airplane .


Highlander

Engine Problems!!!!
 

I've seen two .46fx's do this and we replaced the fuel line from the needle valve to the carb with a good silicone line and the problems went away. I think that the line leaks air on the nipple on the remote needle.

Engine Problems!!!!
 

I have tried all that. I agree, I shouldn't be having these troubles. Never had troubles with an engine in like this that I couldn't solve. Many many people on here are all having the exact same trouble, so it only seems likely that air is being introduced in the valve somewhere. People keep saying it can't happen, but it is happening. I agree, OS used to be a top notch engine. Notice, I said Used to be!

Engine Problems!!!!
 

I almost had to reread this entire thread since I assumed, by the amount of engine problems, this was an MDS thread. Kind of suprised of the negative experiences people are having with some OS engines.

Nik, what do you mean by "maybe the needle valve"? It sounds like you are runnining your engine too lean and I'm guessing if it isn't a partially clogged carb or a fuel delivery problem then its gotta be your needle settings.. Rotate the large needle valve sticking out of the carburertor in the counterclockwise direcdtion about 1/4 turn and then verify you are slightly rich (about 300 rpm shy of max lean rpm) with the pinch test (do a search here for pinch test). You probably are wringing out your engine on the ground and when you fly, the ever decreasing fuel head causes a similary increasingly lean mixture througout your flight until you reach a point which results in a too lean mixture and a deadstick.

The OS engines are extremely user friendly and switching to another brand for future purchases will not help. This is a great time to learn how to tune your engine.

A fuel filter inline with a fuel line to your carb is another failure point. Your are better advised to install one in your line from the fuel pump.

If you suspect the carb is dirty, just remove it, take it apart and clean it throughly. Yes, you can even use water and dishwashing detergent to clean it. Just lightly oil everything when you put it back together.

Engine Problems!!!!
 

oh my, my head hurts. I'm going back to kites.

Engine Problems!!!!
 

downunder,
I agree, the length of the glowplug shouldn't matter, and I was really surprised to see this OS .46FX go from not running well to running perfectly with just a change in plug like that. As far as I know, the two plugs are roughly in the same heat range. Anyway, it fixed it, much to my surprise.

SpaceClam,
Actually, you have that backwards in an ABC engine. In ABC engines, the liner expands faster than the piston, that's why a good ABC engine binds at TDC when cold, but doesn't grind itself to death when running. The running temp causes the fit to loosen a little. This is also why it's bad to run an ABC engine slobbering rich or even at idle for a long period of time with out getting it warmed up first. Cranking away with a starter is bad too. Most ABC engines, if you over heat them, just loose power and arn't harmed. They don't seize, usually (It's possible to get varnish buildup on the sides of the piston that can then jam things up. That varnish gets there because of the overly loose fit of the piston-liner when over-heated).

What you are thinking of is ringed engines, where the ring expands faster than anything with heat, increaseing compression. An overly lean run can easily cause the engine to seize up and create a paperweight. Iv'e seen that happen.

Also, our model engines do not actually require backpressure to run. Engines were run for many many years with no muffler at all and they ran just fine. I've had mufflers fall off in flight, and the engine runs fine. LOUDER, prodcues more power, but otherwise fine. It is true that some engines draw fuel poorly with out muffler pressure to the tank, though I doubt this is the case here.

Highlander,
It sounds like you have a lot of experience with a lot of different engines, and moreover, it sounds like if you are with out an engine for 2 weeks while a service department does it's thing, you have other planes to fly. I agree that if an engine is actually faulty it should be sent back, and it sounds like you'd be a good judge of when to send it back or not. But for a beginner, my guess would be it's not set properly first, and faulty second. So before he ships it back, I'd suggest getting another set of eyeballs on the problem, and if it still won't run, then it's worthwhile considering sending it back. And yes, I've seen some really funny "bad" engines. One engine a friend of mine had, the engine mounting holes weren't drilled. On another, the muffler outlet wasn't drilled out.

On RNV assemblies, on my OS .40LA and .25FXs, I don't have any problems. As someone else suggested, try changing the fuel line between the RNV and carb. It's realy easy to get a pin hole in there. I holed one of mine while mounting the engine. Also check to make sure the bits are all firmly screwed together, and seal the needle with a bit of fuel tubing.

When I have a choice, I prefer the conventional needle valve, and I like carbs like the Magnums that allow you to convert it back and forth between the two arrangements. IMHO, that's what OS should have done, given people the option.

Engine Problems!!!!
 

fx series are not abc, they are abn. Second of all, When you take the muffler off a 2 stroke, they will not idle well if they will idle at all. Without the backpressure, the pressure behind the piston just above the botom of the stroke will be much higher than it is on the top. That causes them to idle poorly. Haven't you seen those early rc two stroke motors? they have no muffler, but they have a mechanically operated valve at the exhaust. It is almost completely closed at and idle, and fully open at full throttle. I don't know why people are having that air bleed problem. this is not the first thread about these fx series having that problem, but i have never had it myself. However, fuel tubing, silicone glue, form-a-gasket, thread locker, teflon tape, and even epoxy would fix that problem.

Engine Problems!!!!
 

ABC and ABN engines work by the same principle. Yes, I am aware that OS using ABN to save a few bucks and make some extra cash. (Nickle being less expensive than Chrome in general)But the expansion principle is exactly the same, the liner expands faster than the piston. Nickle and Chrome are simular metals when it comes to thermal properties, which is why OS can do it this way. OS engines, in particular, are known for having an interference fit when the piston is at TDC, very very tight.

When you talk about the piston being just above BDC, do you mean on the downstroke, or on the upstroke? On the down stroke, just before BDC, the engine is in the intake cycle, and the pressure created in the crankcase is what is pushing fuel up the transfer ports and in to the cylinder. You're saying the back pressure helps push the piston down, but it also keeps the fuel-air mixture from coming up the transfer ports, not a good thing. Too much backpressure, and fuel shoots backwards out of the carb.

On the upstroke, the piston is going to create a vacume in the crankcase that draws the next fuel charge though the carb. I don't think this is what you're talking about.

The earliest throttles were nothing but an exhaust restrictor, no carb at all, because producing back pressure slowed the engine down and acted like a throttle. I don't know for sure why there were engines with both the carb and exhaust cover, but I can think of several reasons why it might be a good idea that aren't related to creating back pressure itself. I'd think it would be because it improved fuel draw. With the introduction of mufflers that provide pressure to the tank, exhaust restrictors went away.

I haven't tested it, but I'd be willing to bet that an engine will idle better with out the muffler than with it, assuming you remove the pressure line to the tank when the muffler is installed. After all, all those big gasser 2-strokes have been running with out a muffler at all for a long time. The're only going to mufflers now because of the noise.

The only time back pressure helps the engine run (other than using it to pressureize the tank) is with a tuned pipe, and that's a different story all together.

engine problems
 

Amen the suggestions to look inside the tank for leaks. I have a .46 LA that always seemed to lean out and lose power after flying for several minutes in the air. I never found the clunk reversed but finally removed the clunk line and found a small pinhole at the inlet and a small slit at the clunk. Engine runs fine now.

Engine Problems!!!!
 

Mine doesn't idle well without the muffler, It isn't reliable at all without it. However, someengines won't even idle without it. a couple of times i have been at the basin when low and behold, off comes a muffler. They idle it down to land it, and their engine dies at about 1/4 throttle. a part of that non-reliability at idle without mufflers is indeed fuel draw. Because there is so little air coming through the carb, it does not suck enough fuel. However, with the big gas engines, They draw enough air that they will suck fuel at idle, But you will notice an increase in throttle transition by putting pressure in the tank or putting a pump on it.

Engine Problems!!!!
 

Ok guys!
I installed the air filter and just flew it! No Problems!
Flew for 10 min in hard wind and the engine did go strong (Changed the needle thing also)
I am really enjoying this plane!
Thanks for all the help and suggestions!

-Nik