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  1. #1

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    ST 90 won't stay at idle..quits...frustrated...

    I have a old S90K with new style carb.Using 10% Wildcat fuel,Fox glow plug w/idle bar.Hi speed runs great...really turns up....but bring it down to idle and it quits rather quickly.Started messing with low speed needle.Didn't want to but ....it's a brand new carb so i figured it ought to be set right from factory.... but.....So have taken low speed needle in at least 1 full turn to lean up the idle.It's better but still not great.Really slow and sloppy transition from low to high.If you keep the ni-starter on it it runs great.Good transition,good idle,good hi speed . So at idle i noticed a lot of bubbles in the line and it really shook and vibrated alot ...then it would quit.
    So what do you think?Suckin air.?..hole in the carb line? Another thing is the tank is not padded.No foam under or on top or sides...completely sourrounded with wood.It's a Big Stick 60 ARF.Fiqured i should cut me a hatch on top and sourround the tank with foam.....but what about that idle.Haven't checked the line yet to see if it has a hole.


    Dave

  2. #2

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    RE: ST 90 won't stay at idle..quits...frustrated...

    Check your manual. Pretty sure it's tells you to screw the low speed needle in all the way, hook up a long piece of fuel line to the fuel nipple, blow into the line and open the needle until air JUST starts to go through. That is the starting point for the low speed needle. it's very small increments either side of there.

    My Italian ST engines have that written in the book...yours should too.

    Don
    Revver Brother #94

  3. #3
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    RE: ST 90 won't stay at idle..quits...frustrated...

    Bubbles in line will cause the engine to die. If the bubbles go away at a certain RPM then they are probably coming from vibration of the fuel tank. If they don't go away then there is an air leak in the tank somewhere. Could be a  flexible line outside or inside the tank, the tank stopper , or one of the hard lines. I think the carb is OK but you have an air leak somewhere upstream . If you have another tank set-up just replace the entire tank and external lines with new. If not ,remove the tank and external lines and submerse the tank in a bucket of water and add pressure through the line that goes to the carb and check for tank leaks.
    Brian Ray

  4. #4
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    RE: ST 90 won't stay at idle..quits...frustrated...

    Here's how to adjust your carburetor: http://www.rcuniverse.com/forum/m_1579985/tm.htm

    Also, don't try to idle at a too-low RPM. Anything below 2,500 is good. Trying to get a super-low idle RPM will only cause problems. Also, go to a fuel with 5%-10% nitro as the maximum. 0% nitro is also good. More than 10% can cause throttle handling difficulties.
    Bill Baxter, Manager Hobby Services/Futaba Service/North America
    3002 N. Apollo Dr. Ste. 1 Champaign, IL 61822 USA
    Service Phone: 217 398-0007
    Email: hobbyservices@hobbico.com

  5. #5

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    RE: ST 90 won't stay at idle..quits...frustrated...

    First, no carb is adjusted from the factory. Second, take the carb off and look through the bottom. You will see a "cats eye" cut in the brass going across the carb. Adjust the low-speed needle so it is half way across this cut out. This is just a starting point.

    You sound like you've not got a lot of experience with glow engine tuning. I would really suggest that you find someone who is used to ST engines. I love them and have very little trouble with them. Also, I use an OS type F plug in all my Tigers.

    paul
    Gosh, model airplanes are not a matter of life and death - they\'\'\'\'\'\'\'\'re more important than that!

  6. #6

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    RE: ST 90 won't stay at idle..quits...frustrated...

    The OS F is a 4 cycle plug.And it's longer than say a OS#8 or 6.What can i expect with this plug.Is it a hot plug.
    I've been out of the hobby for about 10 years now.Have just got back into it this summer but my experience with glow engines is not vast but not a rank beginner. Most of my experience has been with gas engines.I've always read that the low end needle is always set properly at the factory. Don't really know if that's true.

    Dave
    ORIGINAL: RCPAUL

    First, no carb is adjusted from the factory. Second, take the carb off and look through the bottom. You will see a "cats eye" cut in the brass going across the carb. Adjust the low-speed needle so it is half way across this cut out. This is just a starting point.

    You sound like you've not got a lot of experience with glow engine tuning. I would really suggest that you find someone who is used to ST engines. I love them and have very little trouble with them. Also, I use an OS type F plug in all my Tigers.

    paul

  7. #7

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    RE: ST 90 won't stay at idle..quits...frustrated...

    According to OS the F plug is a medium heat range plug. They just seem to work well for me and I've seen several other posts where people use them for ST engines. There may be other plugs that work well also - I just stick with what works for me.

    Paul
    Gosh, model airplanes are not a matter of life and death - they\'\'\'\'\'\'\'\'re more important than that!

  8. #8

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    RE: ST 90 won't stay at idle..quits...frustrated...

    OK so i've tried everything...almost.I tried some 5% Wildcat fuel.A hot #6 OS plug.Didn't like it.I have adjusted and readjusted the low end.Took the carb off engine and looked at "cat's eye" and set low speed needle in the middle.High end ran good but still no good idle.Idle was very rough and i had to keep it very high just to keep it running.Flew it on a saturday and almost crashed into a fence because the idle was so high.Next day i tried again.I changed props from a Master Airscrew wood scimitar 13x8 to a MA K series 13x8..heavy prop.The engine ran and stayed at idle.And idled pretty good..better than i've ever had it.After a bit od tweeking it was running very good.Ended up running best back on the 10% fuel and a Fox RC long plug. Could the "flywheel effect" have made the difference? It was the only thing i changed...a much heavier prop. Dave

  9. #9

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    RE: ST 90 won't stay at idle..quits...frustrated...

    the heaver prop will sure help the idel. they most always do. i would stay with it. i have a italian 61 super tiger motor on a bel- air biplane. the plane is a great flier. the st motor runs great. i have had the ones from china too. compaired to the st i have the china ones ....suck. it's a shame they couldn't match the italian ones. i been flying this motor for two years now. i wouldn't trade it for 10 engines made in china. i will never sell it. it starts and runs like an electric motor. just wanted to let you know. look around for one made in italy. you won't regret it......RON

  10. #10
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    RE: ST 90 won't stay at idle..quits...frustrated...

    ORIGINAL: geeter

    (SNIP) i have a italian 61 super tiger motor on a bel- air biplane. the plane is a great flier. the st motor runs great. i have had the ones from china too. compaired to the st i have the china ones ....suck. it's a shame they couldn't match the italian ones. i been flying this motor for two years now. i wouldn't trade it for 10 engines made in china. i will never sell it. it starts and runs like an electric motor. just wanted to let you know. look around for one made in italy. you won't regret it......RON
    There is a bit of HISTORY here. In June, 1986 +/- (forget exactly) World Engines, (John Malony) the importer of O.S. and S.T. was going bad medical-wise. His Heirs were not interested in keeping WE or their subservant Indy RC going so John sold "Great PAINS" the import rights to OS and ST, for 10 Million yankee greens.
    GP took the mfg tasks to China. Sad as WE had some great engines for different types of modeling. GP stuck with the everday sport flier. Those STs that have a bolt-on front case are absolutely the best of ST. There are smaller excellent engines but for the .60 up, the bolt on casers were - and still are - far better than anything GP has to offer.

    GP made out as GP cut the STs down to poorer quality and thus no competition between ST and the HIGH PRICED Spread, OS. [:'(]

    Tower, at first a small college-kid side business, was assisted by B. Paul (very big distributer in Philidelphia, PA) to get big and set up Great Plains, Distribution company.
    GP had some big money backing it up, so they went out like Sears and Roebuck did, in and after WWII gave big contracts to all the small manufacturing companies that no longer held government Defense contracts. When these small model airplane kit mfg. people received big orders from GP, they kind of deserted the normal mfger. wholesaler retailer ways and went right to the dealer and hobbyists, and now the dealers are suffering and sliding off the trailer. Great "PAINS" and Tower is getting a taste of their own medicine and so will all the hobbyists do same in the not-too-distant future.

    As far as the Super Tigre, the .15, the .23, the .29 all were great little power plants.Where are they now? I have some, Do YOU?

    Super Tigre, before GP, provided a restrictor for the carbs for .35s and .40s and possibly the .45. Without the restrictor the current .40s are a bear to get tuned, With the restrictor they are a *****-cat. I made a number of restrictors for club members. All stated that the restrictor did the work big time. I asked GP why not include them in their engines. NO ANSWER, NO DISCUSSIONS. I run STs in all sizes except the 2000 and 2500 but I own a 2500 still in the box for years. I get every ST .60 (61) Blue-Head I can find on eBay. No idea why because they are nearly impossible to wear out. The .75 is a fine engine, but for some reason the .90 sucks.

    IT's all in the money. GP alaTower has all kinds of OS engines. OS is the prima-dona. Look at the price of a truly fine engine, thunder tigers, priced ahead of like OS. When GP bought ACE RC, the TT went from $50 to 150+/-, then shortly back to $100. They do protect the OS line.

    Had enough? Never meant to go this far! Have a Merry Christmas and all kinds of nice holidays. Forgive me all the typos and even be nice GP!
    Horrace Cain AMA L-93

    β€œPeace is the brief glorious moment in history when everyone stands around reloading.\" T. Jefferson

  11. #11

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    RE: ST 90 won't stay at idle..quits...frustrated...

    Before you even start make sure the carb and lines are free of any debris. Use a good fuel filter such as the Dubro Final filter. Be sure to fill and defuel between the filter and the fuel tank never between the carb and filter. One of the most important things you will do is to rinse your tank before putting it together look next time and you might find some swarf left from the manufacturing process.

    It doesn’t hurt to filter the fuel going in with another fuel filter inline on the filler hose on your fuel pump.

    You can use this initial set up on all 2 stroke and most non pumped 4 stroke engines.

    Note with ST carbs start with the cats eye facing straight down. Later swinging it away from the down position will effect transition from idle. The best plug is a McCoy mc14

    1. Open the high speed up several turns.

    2. Using a 1/16 th drill or steel rod close the carb until the barrel just holds the rod in
    place. Do not force. This simulates a near idle opening of the carb.

    3. Place a piece of fuel tubing over the inlet nipple and blow through. Close the low
    speed needle until no air will pass then back it out until you just feel air passing
    through the line. You will not hear it but feel it by mouth.

    4. Now carefully turn in your high speed until it stops and back it out about 2 to 2 Β½
    turns.

    5. Start the engine and slowly open to full throttle. Adjust the high speed. You may have
    to leave the glo plug on until the high speed is adjusted lean enough to run without the
    glo driver but it is important to adjust the high speed with no assist on the glo plug.

    6. Once the high speed is set slowly reduce the throttle to see how slow it will run. If it
    begins to load up and sounds like its going to stop place the glo driver back on. If it
    picks up and begins to run better then the low end is to rich turn it in 1/8 turn. If it quits
    or there is no change it may be to lean try opening it up 1/8 turn. You will now have to
    return the engine to full throttle to clear it of any access fuel then repeat the process
    over until the engine will idle. Once you get the engine to idle and run wide open you
    need to fine tune the low speed for optimum transition.

    7. To adjust the transition from an idle without glo assist slowly and smoothly advance
    the throttle. Hesitation and excess smoke means the low speed is still rich lean it no
    more than a screw driver blade width at a time. If it quits suddenly when the throttle is
    opened it usually means it’s to lean so richen it up the same way one screw driver blade
    width at a time. Continue until you get the best transition at the fastest throttle
    movement that would duplicate your servo movement. Some new engines require
    break in time before you can achieve perfect transition so you may have to resort to
    slowly advancing the throttle until the engine is broken in.

    Dennis

  12. #12

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    RE: ST 90 won't stay at idle..quits...frustrated...

    got this engine running pretty decent. I have found that a little goes a long way on the low speed settings.It still doesn't have the best transition from low to high speed throttle but it stays running.I may need to adjust the spray bar a bit more.Have been using a McCoy MC59 plug and 5% Wildcat fuel.Have tried Fox long w/idle bar,Miracle Plugs,OS 6&8.The McCoy seems to be best right now.The heavier prop has also helped.I am using a APC 13x8.I weighed a APC and Master Airscrew and the APC was heavier.Haven't run the MA prop yet but it should do better than the light wood props i was using.

    Thanks to all who posted help to me...............................Dave



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