Before you get any further, yes I know I should have bought an OS instead, but nevertheless...

I have a .90 Super Tigre that is only about 6 months old and I've run about a gallon of fuel through it, but I cannot get a decent, low idle regardless of adjusting the needles. The best I can muster before it shuts down on me is about 3k - 3,2k rpms, which I feel is well above the specs of 2,5k rpm for idle.

Also, the highest top end rpm I can get is about 13k rpm. Is this the expected top on the ground? I know it will unload in the air and achieve a higher rpm reaching towards the 16k spec, but 3k rpm seems like a big gap.

Any ideas on how to improve the performance?

Or am I just being too picky in general or because I am expecting more from a Super Tigre than I should.

Thanks.

Hi!
Top rpm and low rpm with what fuel and prop???

For most sport airplanes a 14x6 prop is what ought to use. Preferable APC or RAM. With this prop you can have your engine run as low as 1900-2000rpm provided you run the correct glowplug and fuel and have the tank placed at the correct position...and of course have set the low speed needle correctly!

Fuel: All two stroke engines run good on just 5% nitro! No more nitro is required!
If the Super Tigre is made in Italy, don't use any more than 10% nitro!
Glow plug: OS 8 or Enya 3.
Tanks size: 12-15oz placed according to "the tank rule law"! Preferable with Uni-flow set-up (two clunks).

I agree with Jaka, but will add this:On Supertigre engines, .75 and up, use <span style="color: #ff0000">LARGE</span> fuel tubing so the engine can drink. Using medium or small tubing is the equivelant of drinking a milkshake through a coffee stirrer. You must use <span style="color: #ff0000">LARGE</span> fuel line from the clunk to the carb. Replace your clunk line with <span style="color: #ff0000">LARGE</span> fuel line, and it would not hurt anything to drill out the hole in the clunk a couple of drill sizes larger.

Thank you both for the info. I will make some changes and see where it takes me.

Look at the size of the hole in the fuel inlet nipple on the engine. There is little point in using tubing with a bigger inside diameter than that.

Ed S

Thanks Ed. I'll take a look at that.

Hi!
I'm certain the fuel tubing cannot be the problem. Why should Super Tigre engines demand large fuel tubing when all other engines can use medium size tubing..?

I have a supertigre 90 engine that I also had trouble with when new. I bought it about a year age and have it in a Patriot XL. I have run about two gallons of fuel through it and now it runs great. I had the usual mid range rich problems, and the idlewas not always dependable. I run a 12-8 or a 13-6 prop on it. It idles about 2000 to 2200 RPM. The top RPM with these props is right around 13000. As far as your idle problems, I think I would try the "pinch test". This will tell you if you are rich or lean on the idle. I suspect you may bealittle too lean on your idle setting. ( I just went and checked my idle setting and I am running exactly 2 turns out from fully closed ) I would start with an idle setting of 2 1/2 turns out and see what happens. Of course you set your high speed first and then work on the idle speed. These engines are not the same quality as an OS, but they are about half the cost. They take a lot of break-in time and a lot of fiddling to get them right, but once you get them right, the just might become one of your favorite engines. I know my ST -90 is. Let me know if you need more help.

I just went through this with a new .91 Super Tigre from Tower. Messed with it for 3 weeks and a gallon of fuel, finally said enough is enough and put a Perry 4500 carb on it. It is now perfect, idles, transitions smoothly to full throttle with no hesitation, chop throttle, back to idle. Runs like an OS .91. I am using an OS F glow plug.

Ken

Ken,

I may look at the carb replacement. Where is good place to pick one up?

Keith

I have three ST 90's running like a charm. Two are in cowls on a twin so I can't check the needles, but the third is set as follows: 14-6 prop, 10% nitro, 18% oil in the fuel, muffler pressure, high speed needle 1 3/4 turns open, low speed needle 2 7/8 turn open. Needles checked with throttle barrel fully open.
Chuck

Hi!
All you have to do is set the idle needle on the carb correctly!

While I think everyone in general would agree with this statement as applied to any engine. True if anything is done correctly it "should" in theory work right, but alas the ghosts in the machine hold us at bay. In some cases it is easier said than done. I have fiddled with the low speed needle on my ST90 for far too long and gotten nowhere. I even contacted the manufacturer to ask about the low speed because according to the instructions it is set at the factory and should not require any adjustment. That was the same response I got directly from them, but obviously it was not otherwise we would not be having this discussion.

One other thing to look at - muffler pressure.  I've seen similar problems in setups where there wasn't sufficient back pressure, particularly at low throttle settings.  Pitts mufflers are notorious for this.  if you have a Pitts muffler in you set-up, you might try plugging one of the outlets and see if you get a better needle response and more reliable low idle.  Also use the shortest length of tubing you can between the fuel tank and the carb, and make sure there are not sharp bends or twists.

Finally, disassemble and clean the spray bar assembly to make sure you don't have a small particle caught in the spray bar.  It may not be large enough to prevent fuel flow at high throttle settings, but it might be restricting fuel flow at low settings.

Brad</p>

Hi!
The needles on any engine are not set correctly from the factory...they are just set so that the engine will run, but this setting is not the ultimate. The best setting is always set by the user. Set it by ear!! If don't know how ...take help from someone who can.

Use 5% nitro and either an OS 8 or Enya 3 plug. Too much nitro and the engine setting will be very critical due to too high compression.

Use a 10x6, 11x5 or 11x6 APC or RAM prop..those are the best. 10x6 on a Q-500 type model and 11x6 on a high winged trainer type model .

Iwas thinking along Jans line of thought until he came to his prop selection. This is for sport and not racing. Asmaller lighter prop will and does effect the idle, it's a .90, not a .46. The 14 inch prop would be a better starting point then testing different sizes to find out what works best for engine and pilot/plane.
Irun the SK .91s and anything smaller then a 15 inch prop makes the engine run lean. This is an apples and oranges thing though, the SKs are high torque low rpm engines so a bit different. My older .91s all ran better with props in the 14 or 15 inch range, no racing involved though, just sport flying.

Hi!
Sorry! Thought it was a .40.
For a .91 twostroke, 13x8, 14x6 or 15x4 APC will suit most airplanes

Hi Keith,

I got the Perry 4500 carb off of ebay. It really straightened out the engine. Had a couple dead sticks with the original carb, but with the Perry, coming back to idle for 15 to 30 seconds is no problem. It then transitions back to part or full throttle with no problem.

Ken

I have a ST 90 It ran well out of the box the idle settled down after about 6 tanks of fuel, the only issue I had was the muffler It fell
off the stub on its first flight lucky for me I managed to find it, I fixed this issue by drilling and tapping a 3mm bolt throught the stub and the muffler :- &gt;no more problem

This link may be of some use

http://www.lymanslack.com/Articles&amp;Archives/st.htm


Johnkpap

Thanks for the hyperlink. Now if we can only get manufacturers to take this kind of responsibility for their productsand provide such great detail.

I've got a super tigre 90 and found that a APC 13-6, wildcat 10% nitro,fox long plug with idle bar is the answer. yes I screwed it up in trying to adjust the spray bar to lean the mid range but put it back to straight and inline. The newer spray bars are not tubular (round) as the old ones were when you could twist the old ones and get mid range results. don't do it the newer chineese made supertigres have a flat spray bar instead of the old round spray bars. What I have found is that the super tigre carbs are more reactive to the changes of the low needle affecting the high needle adjustments and vice versa. AKA if you lean the high needle you very much affect the low needles adjustment more that with any other carb I've ever encountered (almost directly). This does make the engine more difficult to tune for obvious reasons. Don't over prop it and use a fuel that has at least some castor (wildcat 10%) excersize much patients and you'll get it. My engine (now) runs like a scalded ape and was finicky in getting it tuned properly, tweak  it like a Ferrari, I guarantee it "can" run just as well. This engine has a big time wow factor you just need the patients to find it. I was initially very dissapointed now I'm on the jazz. Hey you only paid low dollar compaired to an OS, you must re- pay the price in time to tune it properly. mine is now Awesome and is "more" than equivelent to an OS. ON THE JAZZ but it took patients.  

Irontiger, Thanks for bringing that ST .90 posting to the forum. I have several and have not ever been pleased with them. OTOH, the .75s are all sweethearts along with the .60s being good and the .51s are super. The .40 needs a restrictor in the venturi which when they were being built by ST such was supplied in the package. GP kind of did away with such when they took ST over. I make my own and a ST 40 will last for years.
Back to the .90, as I went to your question, and I saw the forum was very old, I started to click it off when I saw the above article stating Lyman Slack as the man to see. Having known Lyman many years ago when we were in the B-47 back in the late '50s, early '60s, I just had to go there. I just printed off his expertise and maybe I can resurect my several .90s.

Lyman Slack is a modeler second to none. He can just breath on an airplane kit and it blossoms into a beautiful work of art. I work and work and someone might ask, "Did you find that in a trash can at the field?" [:@] [:@][&o]

Thanks again for your post and to Johnkap for the link albeit years ago. It still works.