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.

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.

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?

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.

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

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.

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!

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.

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

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.

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.

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.

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.

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.

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

I believe you said you have both makes. - OS and TT.

I have two trainers...a Telemaster 40 w/ an OS 46FX, and an Eagle 2 with a Thunder Tiger Pro 36.
The Thunder tiger is used (Ebay) and fortunately it runs like a Swiss watch, starts with a hand flip. Great engine.(bought a used TT Pro 46 too).

I have been breaking in the OS 46FX since early spring with 5%, and didn't notice a problem until I attempted to run a complete full tank recently.
(Of course by now it was a lot more hot and humid weatherwise than when I started).

I was trying to get a complete run and use a full tank but just couldn't keep it running.
Everytime I tried to go past 1/3 throttle it would sputter and die.
I checked the usual suspects, fuel lines, tank fittings, correct set up, glow plug etc.
No improvement.
I noticed how hot the motor was, and figured I must have the needle set too lean to get that high rpm sound.
(I had read here that breaking in an ABC engine too rich is bad, the engine needs to run hot to break in effectively).

Well after a few frustrating attempts, I let it cool and changed the needle setting (counterclockwise to richen it).
On my set up, a closed needle valve is at a 3:00 position, the way I was running it was about 9:00, so I reset it for 6:00 position, not as high an rpm sound - but you know what, not only did I run a full tank to empty, it ran great the whole time, never conked out, and the transition from low throttle to high was smooooothh.

And I could run it at full power as long as I wanted with not even a cough or burp.

Ok, so I'm new, maybe I'm wrong, but I figured that at the lean setting I had before, the engine must have been getting hot when I raised the throttle setting - and sagging until it stopped.

The reason given for the old exhaust baffle was to retain heat in the plug at idle. Any added back pressure was an unavoidable consequence. Back pressure on any engine is NOT a good thing but unfortunately is necessary nowadays simply to provide enough muffler pressure for full throttle operation with the too large carbys that are generally fitted.

Well, this is the thread I have been needing to read for quite a while. My Hobbico Superstar came with a 40 LA. It started and ran beautifully the first few times it flew. Now it is running rough and quitting in the air after about 5 minutes. It is really putting a damper in my learning curve as I only get half a flight in. I did run it with a OS FS-40 four stroke for several weeks and that ran great. But that engine is now in another plane. Here is what I have done with the 40 LA: Dismantled and cleaned the entire engine, carb and needle valve, replaced the fuel tubing to the tank with larger diameter and a filtered clunk, and just last night I cut away at the plane to allow the tank to be raised up about 1/2". I was thinking I needed more fuel pressure. I was even considering getting a Perry pump. I have fiddled extensively with the needle setting and the air bleed. I have tried several glow plugs. I've tried running with muffler baffle removed.
Anyway, reading this thread I think my next steps are to check for leaks at the needle valve and carb. Unless anyone here would like a near new 40 LA on trade :-)? I wish OS would provide more in the way of troubleshooting, But then OS does have one of the nicest web sight of any other engine manufacturer.

FR

If i said i have tt, i made a mistake. What i meant to say was i have os, but have heard great stories about tt as well.

Now this is weird. Last night I removed the 40 LA engine from my plane and removed the carb to clean and check. And what happens? At least a half ounce of oily fuel comes pouring out. No wonder it is hard to start, runs poorly and quits suddenly. I don't think I am running it too rich since I have tried leaning it out til it almost quits. I have a few theories. The first is that my fuel is old (bought it about 4 mos. ago) or dirty from pumping out the tank back into the gallon bottle (I'm down to about 1/4 gallon) or that the engine is for some reason blowing some of the burnt exhaust back down the intake. The last makes sense, since what I poured out of the engine was mostly oil. Lately the engine seemed harder to turn over like it had more compression, but this had to be caused by all the oil in the crankcase. Once it started running it probably couldn't suck the heavier oil into the chamber to burn. Maybe I need a drainplug to drain the engine before each flight :-). I think I will try some fresh fuel and see what happens. Does any of this make sense?

FR

No. What i think is you are running a really high oil content on an engine that can't use it all. Keep in mind, Fuel is stored in warehouses for years until it is needed, i don't think your 4 month old fuel has gone bad. You can try, and while you are at it, get 20% oil content and see what happens.

AllThumbs,
All that shifting of the needle from 3:00 to 6:00 to 9:00 is way too much movement on the needle. When leaning out the needle, make small adjustments, and make them slowly. The engine will not respond instantly. It's quite possible that the peak is somewhere around 1:30 (or somewhere), and you are going right from too rich to too lean with no stopping in between.

You want to run a new ABC engine a temp, but you still don't want to overly lean it out and overheat it. The old break-in for a ringed engine calls for running the enigine in a sloppy-rich "4-cycle", that's what you don't want for ABC, but you don't want to peak it out either. You want to get the engine to just break in to a "clean" sounding 2-stroke whine and leave it right there.

Some of the comments I've seen are from guys who say "well, it ran well yesterday, but not today". The correct mixture setting will vary quite a bit with air temp, humidity, and pressure. So it's always good to richen up a 1/4 turn or so in the morning, start the engine, and re-adjust the needle for the weather of the moment. Or at least start the engine and do a pinch or nose-up test to check the mixture, and go from there. Usually, the weather doesn't change much during a day, but if you do go out early and stay long enough to bake (say, 75 with dew on the grass and a light fog at 7 in the morning to mid-90's and bright and dry by 2pm, you can be sure you're going to have to adjust the needle at some point during the day).

Flight Risk,
I agree that it's unlikly that your fuel is bad, but it is possible. You can make fuel go bad in one steamy humid afternoon by leavig the cap off it all day. Fuel will absorb water right out of the air. On the other hand, fuel can be stored for years sealed up, and be just fine. If the fuel looks cloudy in the bottle, it's absorbed water, and is garbage. It can still make running hard if it has a little water in it, but not enough to look cloudy, but frankly, I'd suspect the fuel later on, after other things are ruled out better. I pump back and forth, in and out of tanks all the time, and it does't hurt anything. Yes, a little oil goes up the muffler vent line and back in to the tank, then back in to my gallon, but it's totally ignoreable.

As for how the fuel got in your engine, I'm going to guess it syphoned in there from the tank. I have a couple of airplanes where the tank is high enough that with a full tank, if the lines are primed, the tank will hapily empty itself in to my engine all by itself. Other than that, some oily residue in the engine is normal, and not to be worried about.

It does sound like you're flooded though, so emptying the engine by tiling it up so it drains out he muffler isn't a bad idea.

SpaceClam,

By the way, a smaller carb throat diameter helps idle and fuel draw, not hurts it. As Downunder said, most modern 2strokes have carbs that are much bigger than they used to be to try to get big power numbers, but they do that at expense of idle.

Losing a muffler in flight will of course cause poor idle. But it's entirely because of the loss of muffler pressure to the tank. If you set up the low speed mixture to be correct with out the muffler pressure, and allow for good fuel draw, you'll find that the idle will go right back to being just fine. The only valid test is to run an engine with muffler but with out the vent line attached and then run it with out the muffler, and see if the idle is affected. As downunder said, backpressure is never good (except tuned pipes)

I understand that a smaler carb draws more fuel, because of the vaccujm caused by the air moving through it. A smaller hole means that the air has to move faster to get the same amount of air through it in the same amount of time. While i am not certain, i will not argue any further whether you can idle an engine without pressure, Simply because all i have seen is muffler falls off=doesn't run well. I am not sure wether it is because of an unequal pressure or lack thereof.

I probably did make too much of a needle setting change, that is true.

I was getting a bit frustrated trying to find a setting to get a full tank run without stopping.
I've been waiting to get a first flight under my belt, and didn't want to have an engine that won't run a tank w/o craping out on me.


Anyway, I have a few questions:

1.) I believe I actually went from a leaner setting to a richer settingg (and not vice versa) as I went "counter"clockwise from a 9:00 position to a 6:00 position (the 3:00 position being the needle closed shut).

The engine isn't running blubbery yet, so I believe it may be rich - but not too rich.

2.) Any chance that I have been breaking it wrong or done some damage by NOT running it lean enough (hot enough)?
I've only got between 3 and 4 tanks of 5% at this point.
And I always tend to worry about running too hot.