mrcoolpop

I have the 60 size Stik with a SuperTigre 90 engine. The problem I’m having is after I take off and get airborne I give it full throttle it flutters and kills. I make sure that its trim out and the mixture is ok before takeoff. Also this engine only has about 4 flights on it. My first flight was perfect. The last three has been again fluttering and then it kills after takeoff. I am now contemplating on getting another engine for this plane. What engine would be good for the Stik without all the headaches? I really like the Stik and want to enjoy my flying.

tessmar

IMO there are two characteristics of Super Tigres that can cause symptoms such as yours. The first is that they seem to take a long time to break in, perhaps due to the nature of the rings versus the material of the cylinders. At any rate, with my two ST motors this was an issue that caused stalling. My ST60 probably had 30 flights on it before I could consistenly rely on it. The only solution until then seemed to be to run it quite rich and with a fairly high idle speed...and to not let it idle for any length of time before takeoff.
The second issue is carburetion. If you look on the ST site for parts data you will note that the carb and its components (including the needle assembly) are identical for the 60 and the 90, and if I recall (not looking at the site right now), one of the smaller model motors (45?) as well. While this might have saved some money it represents, again IMO, an extreme and unhappy compromise. My 90 never ran as well as the 60, and one of the most experienced flyers in our club told me the smaller motor runs best of the three. It appears the engineers tried to design a carb that would suit all three sizes, but I fail to see how a single venturi and needle size could be anywhere near optimal for three motors with significantly different displacements.
The good news is, if all of this is accurate, that the 60, once broken in, is a reliable and quite powerful motor and mine has been flawless after it got over its initial teething pains.

mrcoolpop

Tessmar,
Thanks for in lighting me on such good info on my engine. For as the idling I tried that but it seems to still stall once in flight. One point you did have is maybe I just need to give it time to get broken in for better performance.

tessmar

It might be too lean. Have you tried holding the plane with its nose straight up and giving it full throttle? (You should have a friend help as a 60 is pretty powerful and you shouldn't try to hold it with one hand while advancing the throttle on your radio with the other!). If it leans out try opening the needle a bit. Try to figure out under what conditions does it stall? In particular, what attitude is the plane on? Climbing? flying level? How are you advancing the throttle? Slowly? Or "slamming it" open? Can you determine if there is a "dead spot" in the throttle advance? Does it only happen when the engine is cold? Hot? Either flying or on the ground how much smoke is there? What does the oil coming out look like? Make sure the clunk isn't stuck someplace. Be aware that it willl fly differently (under load) than on the ground or test stand. I'm no expert, but the answer to these should provide some help. I'm not very experienced in r/c motors but these are always the things the "guys in the know" at my club want analyzed when I have a problem. I am pretty knowledgable in 1:1 scale (auto) motors, including port timed 2 strokes (which is what this motor is). Although these are pretty simple, they are very high performance relative to displacement and therefore are pretty sensitive to tuning and fuel/air flow.

mrcoolpop

Bingo,
I think you just hit the mark. Now that you mention it, all the times that it has kill I was always in a vertical climb, always. I need to do what you mention about holding the nose straight up and giving it full throttle. I have never done this before not even at the field. This could be the solution to my problems. This weekend I'll get someone to help me so see it this resolve my problem. Getting excited now can't wait to see what happen. Will PM you on the results.

SeamusG

The ST G90 likes to have the "it's own way".

[*]The G90 likes LOW nitro percentages - many happy owners recommend 0% or 5% and will argue to the death. Diehards for sure.[*]The needle's cat's eye needs to be aligned with the throat of the carb. see pic 1.[*]Have a spare throttle linkage because they are CHEAP.[/list]There a MANYhappy G90 owners out there.

pic 1 - my G90 "inna box"
pic 2/3 - part explosion

Get a couple of #4's - if you have a spare you'll never need it. Just like the guys who take a 30 gal. trash bag to the field to ensure that they will NEVERneed it. How UNTRUEthat is. My LT-40 didn't need the bag but it needs repair - bad battery pack.

For more info check the Glow Engine forum - might even be a Super Tigre sub-forum. Check it out.

mrcoolpop

Currently I use the Omega 15% for fuel. Do you think it would help if I go to the 5%?

jetmech05

Never having a Super Tiger I can only tell you what I've heard...low nitro content......and of course a good mixture...don't try to get full power mixture on a new engine.....things are still mating and will change....making constant mixture changes if you try to run at max power mixture right now....instead as said above run slightly richer until you have at least 10 to 15 flights.....then you can begin to tune for max power...good luck

opjose

SeamusG is right on the mark.

I typically run 5% on all of my SuperTigres and they seem to love it.

Tweaking the "cat eye" as the documentation says only makes matters WORST. It should be adjusted as he said, if you've moved it.

The SuperTigres have a tendancy to have MINOR transition problems.

To get a good transition and no stall outs during nose ups, you must run the low speed rich, and that may lead to the engine refusing to shut off even with the throttle barrel closed, as there is a good bit of air leakage around the rubber boot seal.

Point the nose of the plane up after you've started the engine, hold the plane firmly and run it up to full speed.

Lean the HS needle for max RPM's, then back off 1-2 ticks, no more.

Level the plane and the RPM's should drop a bit. Drop the nose a bit and the engine should slow down further but not stop at full speed.

Level the plane and bring the engine to idle. See if it idles well.

Set the idle a bit rich so that when you throttle the engine up quickly there seems to be no hiccup or hesitation through the mid range.

That MAY mean that idle will be affected ( not all of my ST's require this but many do. ).

Once dialed in the ST are very reliable engines.

Mr. Canadian

I too have a ST G90 that i'm breaking in, and I also run 15% nitro. I used to have the exact same problem as you with the motor quitting in flight and running fine on the ground. I found the best solution for it was to richen the high end, then tune the low-end and keep a high idle. I also like to warm the engine up a bit before every flight.

Phoenixangel

I am a huge fan of Super Tigre engines and I own several. Your 15% fuel is fine all I run is 10-15% wildcat premium extra.

It is very important you allow a lot of break in time on your G90. They will not run properly until after a gallon or so of fuel. During this time you may need to change your glow plug. Break in is hard on them.

Once you get them through the break in period there are a few simple steps to tune them to be the monster they are supposed to be.

From the Super Tigre site.

Getting one of these engines running perfect can be a little tougher then others but they are well worth the effort.

oldtyme

This is not only true of the G90..........liking LOW nitro percentages. I was recently having problems with a well broken in OS91FX and I had to do a factory mod to help it along but the suggestion was there that when you are approaching bigger engines like the 90's/91's they do like a lower percentage of nitro. I have since gone to 10% from 15% and the 91 runs much better and is much more reliable. I do have a ST75 that I had been running 15% in but I'm also going to go to 10% with it too.

Insanemoondoggie

I have a ST.90 that does the same thing, runs great on the ground, but dies at midrange in the air. Tried everything that has been posted so far with the same results. I'm going to try putting mine back on the engine stand and run another half gallon or so thruit, has about a gallon now. If that doesn't do, may try a Perry carb or just sell it super cheap on RCU,give up.and cry uncle.

jester_s1

Mine has great reliability and stump pulling torque. I bought it used, and the seller said it had about 2 gallons in it. With any 2 stroke glow engine, they will run over a fairly wide range of needle settings. Essentially, as long as there is enough fuel in the mix to burn at all and the glow plug stays lit, they will keep running. Mysterious dead sticks in the air are more often fuel tank or line problems or either air leaks in the engine.

skypiratescotty

My Feedback: (32)

Swingin' too big of prop can also cause the engine to die after a few minutes under load. I have a ST75 bought new in early December and the guy at the hobby shop said to put 13x6 on it, so I did. Ran three tanks thru it on the bench with no problems, in fact it ran awesome. I put it on a Pheonix Super Decathlon 40, flew for about 3 minutes and it died. I landed and it re-started right away so I thought maybe air bubbles but no. After another flight with same results I read thru the manual and realized I should be using 12x7 or 8. I got a 12x7 and the engine runs perfect and hasn't died. It also seems to spin up smoother and faster while flying.

I definately agree with everyone else as far as running on the rich side but just something else to think about.

Scotty

Gizmo-RCU

My Feedback: (27)

I have a G 90 that I purchased from a guy who was having your exact problems and was fed up, got a good deal! Broke it in and never looked back. These engines take a great deal of run-in to be right. (had a G-51 that was the same). I run 15% and
never have had a problem with this engine after the initial gallon or so. Don't expect perfection out of the box with most ST's, good value for the price!

opjose

It's also a good idea to use a prop with a relatively high inertial mass until you've run several gallons through the engine.

APC props are good for this. They are much denser than a wooden prop or something like an Master Airscrew prop.

The additional mass helps keep the engine running when it is struggling during breakin and it helps maintain a lower idle speed.

Insanemoondoggie:

Been there... richen the low speed still more, even if it seems like you cannot get a low idle... then try flying the plane... but be prepared to land hot.

If this cures the in-air transition problem ( I bet it will! ) then you may want to use my "fix" for the low idle speed setting.

On similiar behaving SuperTigres I've taken to adjusting the LS richer then making a small half moon shaped cutout at the point of lowest throttle barrel closure. A small round file works fine for this, though you'll temporarily have to remove the throttle barrel to make the cutout.

This extends the LS range slightly while making it a bit leaner... I posted pictures of this on another thread.

The slightly enlarged opening permits you to close the throttle even more, while maintaining a leaner LS mix in spite of the richer LS needle setting.

It cured my transition problems on all similiarly aflicted ST 75 and 91 engines.... though not ALL ST's I have seem to have this problem.

chemie

I have 2 ST51 and they are great. I got a used ST90 and after 2 months gave up and bought a new one. It would just cut out mid flight. Also, I found that to prevent mid-range from being too rich, I was always too lean on the low end which also caused problems in-flight.

The new one is better but still not great. As others have said, you need to have a rich low-end and run a high idle. I still find the mid-range rich and sloppy. I will try a OS #7 (vs #8) glow plug as some have suggested that helps.

PA BEN

I run 10% nitro in mine no problems.

opjose

If I read that right I think that's the opposite of what I've found with the many ST I own.

To get the transitions good, I find you must lean out the HS to get best power, back off 200 RPM, then set the low end VERY rich to get the transitions richer than one might expect, enough so the engine does not cut off when it goes nose up during a transition.

That creates a low idle problem as it is then so rich the engine cuts out at idle, which I solved with the fix above.

Once done the engine is as smooth as silk at all speeds and never ever cuts out.

To rephrase, prior to the fix, to get a good transition I had to set the idle so rich the engine either bogged down, or would only idle at a fast speed....

OR

If I set the LS to get a good idle, I would get a bad transition with a tendancy to cut out when nose up and throttling up/down. Ugh.


But not all of my ST's have required this fix... about 60% seem to work just fine with standard tuning techniques.

Never the less the ST's are very reliable once you get past their tuning quirks.

jester_s1

A lot of needle issues are cause by air leaks at the carburetor. That's not a Super Tigre specific issue, but it does seem that they a touch more prone to it. If there is a leak, it changes the calibration of your needles. You wind up having to go richer on the top that you should, which means that a proper idle setting gets too rich. So then you lean the idle to run right which changes the timing of the needle's withdrawal from the spraybar, which is what controls the midrange. Such an engine will run right on the top and the bottom, but have issues in the middle. Obviously not every problem with an engine is caused by an air leak, but it is something to consider when tweaking the needles just doesn't seem to work like it should.

SeamusG

Will replacing o-rings resolve the leak? Or are the leaks due to poor machine work?

jester_s1

Usually new o rings and pressing down hard enough on the carburetor to compress the o ring a little when you install it will fix it. The o ring has to be springy to work, but after a year or two of soaking in methanol they start to harden and need to be replaced. If you want some insurance, a little RTV silicone around the outside gives you some insurance. The machining is fine on Super Tigres from what I can tell, especially in that area.

Bill Diedrich

Another area that is prone to an air leak is the needle valve itself, having a
very small o-ring in it that after time hardens and will cause some erratic
engine runs or having to constantly adjust the high speed needle, a quick
fix is placing a piece of tight fitting fuel tubing over the barrel end of the
needle valve so that when is is screwed back down and reset it will act as
a secondary seal for that area. Having done this all on my 40, 51, 60, 90,
& 2300 ST's, I have taken at least one problem from the tuning problems
associated with Super Tiger engines, but like stated many times above once
you get them broken in properly, they are a very reliable & pleasureable
engine to own. I have also found that running 0%-5% in my 60 & 90 is what
they prefer and the 2300 runs beautifully on FAI (0%). But the nitro % is
ususally determined by the area of the country one lives in, higher altitudes
may require a little more nitro content than at sea level, also the moisture
content in ones air comes into play. But if you have determination you will
be happy with the end product, a reliable, smooth transitioning power house
that you'll really treasure.

opjose

Exactly, or have an issue at idle and run good on midrange and top end.

The ST sometimes exhibit this. You can adjust for one but not both.

As you said the most probable cause is an air leak. While typically the prime suspect is the "O" Ring seals of the Carb, with SuperTigre engines, that is not the what is the primary culprit.

Rather the throttle barrel cylinder ingests air like CRAZY, which is why SuperTiger installed those rubber "boots" to help seal this area.

( I took a brand new replacement carb that I got trying to solve these problems, then after closing off the intake area with a stopper/seal I put a vacuum on the engine side of the intake "O". Copious amounts of air are drawn in around the throttle barrel cylinder at the "boot". )

The problem is that the boot lets in a lot of air. To overcome the problem you end up richening the engine a lot to get a good transition, but the low end bogs down...

Some people suggest using a second party carb to solve the problem... ( A Perry Carb cures it quickly...) but I'd like to see both a "user" fix and that SuperTigre do something about all of this.