Spoiler

The 120 is installed on a Funtana 90. Large bore tubing and Dubro giant scale filler with BCM pitts muffler, one outlet crimped about 70%, exhaust fuel pressure only. Flown with a variety of props from 16x6 to 17x5.

When new, the motor was stupendoulsy unreliable despite a gallon of run in fuel thru it. A dud F plug caused some more problems but now, with a good plug, the problems are back when using 10% nitro fuel. (Morgans Omega)On 5% nitro the motor seems to be 100% reliable but on 10, it starts fine only to die in the air after 3-4 minutes. Is this likely or possible - I am used to motors that tolerate 0, 5 0r 10%. I am ready to bin the motor as after 10 or more dead stick landings the last of which cost me the rudder hinges and servo gears, I think the plane is on borrowed time.

Any suggestions engine experts??

jamesg25

Well... it is said that Bigger engines prefer, or at least are happy, with lower nitro content. You stated the motor works 100%reliably on 5% nitro. Now i know this is probably not the answer your looking for but just run it on 5% and save the money that you would spend on 10% also I'm my opinion bigger engines prefer Castor I'm not familiar with omega but you could try a few different brands of fuel and see how it works out. also you may have the engine to lean if it cuts 3-4 Min's into flight, too lean and it will overheat. maybe try richening the mixture.
hope this helps
regards
James

Harry Lagman

Spoiler,

I've worked on one of these engines for a guy. It was horribly rich in the lower mid range even though the high end and idle were good.

I bet yours is "flaming out" at mid range throttle settings. You mentioned the OS Type F plug, which we found to be the most resilient with respect to flaming out.

I came to the conclusion in working with this particular engine that the carb calibration is not correct. If it were mine, I'd either machine some mods into the carb barrel to lean off the mid range somewhat or I would fit another carb to the engine.

It's a pity because in every other respect, it was a good engine. It was consistent at full throttle, easy to start, quite powerful and had a fantastically steady 1600 rpm idle. It ran about 8300 with an MA 16x10 prop.

Spoiler

Thanks guys. The 5% - 10% story is not 100% certain. The other variables are props 16x6 v 17x4W v 17x5 wood. On 5% with the 17x5 it worked fine. On a mixture of 5%and 10% with the 17x4w, it died after 5-6 mins. After that as the nitro content grew, so the reliability dropped until the last flight when I had to land at high speed with the wind and clipped the rudder on the runway.

James, Omega is 18% oil and 50/50 castor to synth AFAIK.

Harry, I found that when new, the engine ran badly in the mid range, way too rich and richened more in the air. Its not doing that anymore, so maybe I am leaning it too much. The weather also got hotter as the day progressed which may have added to the problem...

da Rock

This probably isn't it, but it's worth thinking about.

Nitro content affects the timing in 2-strokes. Compression also has some of the same effect. It might be worthwhile to pull the head and check to be sure there is a washer in there. And while you're there, add another one to lower the compression. I've cured a couple of lousy running engines before by dinking with their compression. Truth is, there really wasn't any pattern to the fixes. I just tried different numbers of washers and that worked. It seemed at the time like some mfg's were solving some of their tolerance problems by juggling the washer counts. You'd see 1, 2, or 3 washers in there. And on some of the cheaper engines, I've seen lousy running motors that had none. They wound up running great with just one. I figured the assembly worker decided to up his production by saving a step. chuckle....

Minor changes in nitro content usually don't affect your normal engines, but you've not got a normal engine, right? And if you haven't checked all the bolts on the motor, it'd be worth a moment. I fixed a lousy running engine a week ago just by tightening the head bolts. The guy had bought it used for almost nothing. He said that he'd "paid almost nuttin' for it" and "didn't figure it cost enough to check the all the bolts".... go figure..... Thank goodness the problem wasn't in the backplate seal because he didn't figure it was worth pulling the motor to check those bolts after it ran ok with the head bolts tight.... amazing....

Bax

My Feedback: (11)

The best way to set the engine is to have the idle needle much too rich, and the high-speed needle quite rich. Start the engine at 1/4-1/3 throttle, let it warm up and then advance to full. Lean the high-speed needle to just rich of peak RPM. If it will keep running at that setting with little change in mixture, then it's good. Now slowly retard the throttle and work on the idle mixture. Many people don't get the idle mixture lean enough. You may have to give up some idle RPM to get a good setting. Anything below 2,500 RPM is considered 'good".

Hope this helps.

Flyboy Dave

My Feedback: (21)

I think it's a combination of things....it's overheating. Lower nitro, a cooler plug
and a smaller prop. If the Pitts muffler is not pressurizing the tank completely
like the stock muffler....that could be a problem as well. If the engine is cowled
you might want to remove it until you get it dialed in.

FBD.

NM2K

My Feedback: (14)

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I have bought several engines that had loose head bolts, loose backplate bolts, leaking carb junctions, etc. Some were new, some were not. It's always good to check the bolts.

I would slip an extra head gasket in there and see what happens.

Yes, if he is setting the mixture leaner and the temperature rises, that could cause a problem.

These are ringed engines, aren't they? They take a while to break-in. Until that occurs, all bets are off concerning getting good tractability (transition/midrange) until the ring seats.

No, a difference of 5% nitro increase shouldn't really make that much difference, but if the engine was tight or had high compression from the factory, it will aggravate whatever other problems may be in the soup, such as insufficient run-in time.

Don't give up on it.

This is why I recommend that folks have a break-in bench and a break-in model airplane for finishing the break-in. Don't mount the engine on a 3D type of model until it is a known good runner. Yes, this is a PITA, but it will make flying much more enjoyable in the long run.

If worse comes to worse and the engine persists in quitting rich in the midrange (if that is what is happening), a swap to an ASP/Magnum/SC carb would not cost much. Maybe someone in the club would let you borrow their carb temporarily just to see if it will help.

I wouldn't give up on the engine. Most Chinese engines, even GMS, are good engines once fully broken-in and understood.

One more thing. It is never the engine's fault if YOU, the pilot, crashes the model when the engine quits. You have to understand that good pilots are prepared for every contingency. I'm not trying to be a *****. It is simply the truth. Good luck and let us know how you fare OP.

DarZeelon

Spoiler,


I believe that if you check the [link=http://www.morganfuel.com/omega_blends.htm]Morgan Fuels Omega web page[/link], you will see that Omega fuels are 17% oil, of which 30% is CleanCastor and the remainder, synthetic.


Also, larger engines need a colder glow-plug.

Although OS F four-stroke plugs can be run at a rich mixture setting and behave colder then they really are, it would be better to use a glow plug of the correct heat range. Cold is OS A5, Rossi R4, MVVS C6 and similar.

...And you really don't need any more than 5% nitro, although Tower says to use 10-15%...

Spicoli

ED,
"One more thing. It is never the engine's fault if YOU, the pilot, crashes the model when the engine quits. You have to understand that good pilots are prepared for every contingency. I'm not trying to be a *****. It is simply the truth. Good luck and let us know how you fare OP. "

How are you supposed to save a plane if the engine quits during a hover a foot off the ground?

Dar,
" larger engines need a colder glow-plug"
Why would Jett recomend a OS F plug for their 120L

lloyd a

hi i run 4 of these engines and use morgan fuel in all of them. and yes i do have to use an os-f plug and i use 15% fuel, i use a master air screw 16x6 i am at 2300 ft and find this is the best and most reliable combination to use. found that after all of them had one gallon through them had to lean the low end mixture by about 1/4 turn and then set the high end. any other way would always run into dead stick's. now i must mention that i am also in northern Canada and a warm day here for flying is only 72 degrees farenhiet or 23 celcius

NM2K

My Feedback: (14)

<grin> Planes aren't for hovering, son. That is what helicopters, Harriers and Ospreys are designed to do. Even they crash when the engine quits.

Hovering is not a natural act for an airplane. It wasn't designed by the Wright Brothers for hovering. You'll have to look up Sikorsky, Paiaseki, Larry Bell (and his sister Clara). Most of you young'uns won't get that last reference. <G>

I know IC engines well enough to know that sooner or later, one is gonna give you a "GOTCHA". I don't care how careful and meticulous you are, an engine will quit on you one day. If you insist upon doing maneuvers like that, you have to be ready to bear the consequences.

I do my hovering mostly on a simulator and a few electric models that I own. I can think of a lot better things to do with my money than to bet it on hovering an IC powered plane that I know is going to quit sooner or later. But we all have to make our own decisions.

XJet

Ed, you're playing devil's advocate aren't you :-)

I spend a lot of time hovering airplanes -- defying logic and gravity.

In all that time I've never had an engine stop on me and so have never suffered the consequences.

It all boils down to choosing a reliable engine, making sure your fuel system is 100% and making sure you've got enough fuel left to complete every manuver you start :-)

Oh, and it also helps if you fly a profile -- that way you can see the fuel level as you fly by and even if the engine does stop it's not a big job to fix the airframe :-)

Spoiler

I have checked the head bolts and found them tight enough. I dont think a case airleak is the problem, more like one of the mixture issues mentioned above as the motor has been reliable as I mentioned initially.

I'll change back to 5% and leave the settings alone to see if there is any substance to the nitro argument and then go to Bax's suggestions on mixture set up if it cuts again, and then finally look at the head gasket story.

One bonus, I have had lotsa engine off landing practice. Its a breeze as long as the CG is forward. Just speed it in in a 10deg dive and flare a few " above the ground. This wont work in a hover 3 foot up of course. Thats why I have a spare Fuz sitting in a box at home.

speedster 1919

My Feedback: (3)

Your in South Africa I'm surprised your using 10% nitro. Usally only Americans are nitro hogs. Dar is right Omega is 17% total oil 30% castor and 70% syn. For every 5% nitro you go down increases your fuel milelage about 15%. The biggest nitro boost is from 0% to 5%. Stay with 5% and set your engines to run good on that fuel. Your wallet will thank you. Don't play around with different fuels. I'm not sure but some engine mfts ship to USA lower compression setup knowing we will use more nitro than rest of the world. OS may due that too. Make sure to hold plane vertical 10 seconds to catch a lean problem before flight.

NM2K

My Feedback: (14)

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Yeah, you caught me. <G>

NM2K

My Feedback: (14)

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Please don't become one of those guys that "leaves the settings alone". No wonder your engine is quitting.

Glow engines need to be adjusted each and every time they are started for the first time of the day. In fact, if you are flying all day long, you should recheck your needle settings once or twice more that day. Usually just the high speed needle will need tweaking. The low speed stays pretty much good to go, but this is only a generalization.

A glow engine's ignition "timing" is affected by ambient temperature, humidity and air pressure. This means that the carb settings constantly need to be readjusted in order to keep the timing where it should be. Yes, glow engines have "timing", even though it isn't apparent at first, compared to gasoline fueled engines.

The good part is that after a while, you will only have to hear the engine run for a little while before instinctively tweaking the needle one way or another. The more you do it, the easier it becomes. Soon, you won't even realize that you are doing it.

While the gasoline fueled models do not need this kind of attention, the glow fueled engines do, in order to run reliably and safely. It just goes with the territory. Kind of like getting used to the fuel goop all over your model at the end of a flight. Good luck, my friend. Those preaching against this simply do not understand glow engines - no offense intended.

britbrat

Absolutely agree

Sport_Pilot

IMO the OS F plug is too hot. A cooler plug may allow more nitro. Higher nitro will make the richer midrange more tolerable. Check the tank height and muffler back pressuer. High tank height and high muffler back pressure cause rich midrange.