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  1. #1

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    OS 120 Surpass pumped rich at idle

    Hello all,

    I have an OS FS-120 Surpass pumped engine. It is the version with the regulator right on the pump, center of the back plate.

    It has an issue I can't figure out. It wants to run rich at idle. I have leaned it out as much as the carb adjust allows. And, I received instructions from Great Planes Service that screwing the regulator out would lean the mixture. It didn't. So, I find it is rich at idle and tends to load up. Being pumped, it will not clear the excess fuel when you throttle up. The engine runs strong with a master airscrew 16-6 prop.

    Anyone have any experience with this version of the pumped OS 120?

    thanks
    DW_Crash

  2. #2
    David Bathe's Avatar
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    RE: OS 120 Surpass pumped rich at idle

    I have a lot of experience with the old pumped 1.20 surpass II, don't know if this is the one you have... mine has the pump on the back plate (with a screw in the middle that ISN'T the regulator) and the actual regulator (a square box) on the carb/close by the needle.
    Running rich is a quirk with OS pumped engines BTW.
    PM me if you're still lookin' for answers.

    Best Regards: davidbathe.com
    Occasional Aircraft Illustrations.

  3. #3

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    RE: OS 120 Surpass pumped rich at idle

    David,

    My version has the screw in the center of the pump and no regulator on the carb. It is the earlier version. The carb does not have a venturi.

    Running rich is normal? Really!!!

    Dave

  4. #4

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    RE: OS 120 Surpass pumped rich at idle

    Go to the LHS (or the sprinkler aisle at Home Depot) and get a couple of Tee fittings. Install one between the pump and the carb, the other in the return line to the fuel tank. Use a piece of fuel tubing to connect the two tees.

    The SurpassIIs pumps put out too much pressure at low rpms. This fix allows the excess to go back to the tank, yet still provides adequate fuel flow at high rpms. I always ran the straight part of the tee (the top) as the carb and pump connections, and the 90 degree leg as the bypass.

    I've done this to at least 5 SurpassII 1.20s with complete success. It even worked for inverted engines.

    Best $5 fix you'll ever find!
    Trent Combs
    Fly \'em until the last piece stops!

  5. #5

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    RE: OS 120 Surpass pumped rich at idle

    I have a short sidebar article by Clarence Lee in one of his engine columns in which he repeats a fix someone told about fixing the rich part throttle condition of the surpass II pumped engine. Basically it is to remove the eccentric adjustingscrew and manually lean the low speed adjustment needle and then reinstall the screw, also makes mention of making sure the bottom small hex screw is tightned.

    I can look up the article and repeat it word for word. He claimed it worked well to get rid of the part throttle rich condition due to the high pump output pressure.

  6. #6

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    RE: OS 120 Surpass pumped rich at idle

    Swify,

    I would greatly appreciate reading that article. Can you scan it and post it? Or PM it to myself.

    Thanks a lot for the help,
    Dave

  7. #7

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    RE: OS 120 Surpass pumped rich at idle

    Will try scanning it and posting it tomorrow.

  8. #8

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    RE: OS 120 Surpass pumped rich at idle

    I forgot to bring the article to work with me today, will remember it for tomorrow. I have a 1.20 surpass II that I bought in 1994 it has never been run,the plane I was building to put it in got shelved for a bit over a decade ,started working on it again lately should be finished up soon.

  9. #9

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    RE: OS 120 Surpass pumped rich at idle



    Scanned article attached about the low speed mixture adjustment.

    Attached Files Attached Files

  10. #10

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    RE: OS 120 Surpass pumped rich at idle

    Swify,

    Thanks you very much!!!!!

    Dave


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