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  1. #1

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    Badly running YS 63S

    I have a YS 63S that has had this problem since I bought it used. It is very slow in transition, but not during the first 15 seconds of running. While advancing the throttle I can see raw fuel drops spraying about within the carburetor. You can overcome the problem slightly by turning in the regulator screw nearly all the way but then it runs terrible at top end. It never has idled well. Swapping in a new regulator. which is off a perfectly running engine, doesn't change the behavior. I have replaced the bearings, checked the cam timing, adjusted the valves, milled the valve cover flat, tried multiple plugs, confirmed I have no pressure leaks (multiple times), all to no avail. I know these engines were shipped with different needle valve configurations and am starting to wonder if I have the wrong mixture of parts in the needle valve assembly. The needle valve tip protrudes about a sixteenth of an inch out of the assembly, inside the carb. Yes, all the 'O' rings are new and healthy.
    I've been working on this for two years now. I guess I need help!
    Phil

  2. #2
    petec's Avatar
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    RE: Badly running YS 63S

    Did you verify the air bleed on the throttle butterfly is not blocked/clogged? It would act the same as having the low speed needle fully closed...rich at idle and crappy transition. It will tolerate and even need it when cold but not once it warms up.
    Team YS, Team Airtronics
    Pattern Junkie, Revver Brother #82, Gear Head

  3. #3

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    RE: Badly running YS 63S


    ORIGINAL: petec

    Did you verify the air bleed on the throttle butterfly is not blocked/clogged? It would act the same as having the low speed needle fully closed...rich at idle and crappy transition. It will tolerate and even need it when cold but not once it warms up.

    Um, no I didn't.
    But I sure will tonight!

  4. #4
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    RE: Badly running YS 63S

    Be careful and take note as to how you push the throttle barrel out. The seal is tapered and you need to make sure the higher end is the of the seal it the last part out or the throttle bore will cut it. So you push it out one side and back in on the other.
    Team YS, Team Airtronics
    Pattern Junkie, Revver Brother #82, Gear Head

  5. #5

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    RE: Badly running YS 63S

    Unfortunately, the air bleed channel in the butterfly was wide open clean. I changed the tapered seal while I was at it but it looked fine. My guess is that a bad seal would would cause a too lean situation rather than mine but I swapped it out anyway.
    The old seal appeared fine. I won't be able to test it till tonight. Any other thoughts?

  6. #6

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    RE: Badly running YS 63S

    I had a brand new YS63 with very similar issues.
    Fuel poring out of the carb infact fuel everywhere, just couldn't lean it out.
    Eventually replaced high speed needle.
    Solved. Engine runs perfect.
    YS had shipped the engine with the wrong needle. The replacement was very different.

  7. #7

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    RE: Badly running YS 63S

    I had another needle valve for a 63, which was shorter (ie more tapered). No help what so ever. I'm considering getting a new high speed needle valve assembly, but will wait and see what the moderator says.

  8. #8
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    RE: Badly running YS 63S

    The seal would cause a lean condition.

    Lets go back to square one...OS type F plug or YS #4 plug? You said you tried different plugs I just want to make sure it is one of those, I learned the hard way about using other plugs and it cost me shipping to YS to learn it.

    What fuel?

    What Prop?

    Idle RPM?

    WOT RPM?

    Not discounting the needle valve but that would also make setting the high end difficult.
    Team YS, Team Airtronics
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  9. #9

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    RE: Badly running YS 63S

    Tried both YS and OS F plugs.
    Fuel is 5% castor, 15% Klotz, and 20% nitro. Have also tried all synthetic oil as well as cool power 30% heli fuel.
    Prop, at present, is a 13X6. Runs the same with a 14X4 or 13X4 or 12X6...different top ends of course, same wet transition.
    No idea about actual RPM's but will check tonight.
    Appreciate your interest VERY much.
    Phil

  10. #10
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    RE: Badly running YS 63S

    Let's get the RPM at idle and WOT nailed down. If the high end doesn't lean out properly then we'll hold the need suspect.

    The high speed needle sets the mixture at WOT, the low speed air bleed gets the idle under control and the regulator gets the transition and overall fuel delivery volume set. The fact that you changed regulators makes me wonder though.
    Team YS, Team Airtronics
    Pattern Junkie, Revver Brother #82, Gear Head

  11. #11

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    RE: Badly running YS 63S

    The engine ran so badly last night I didn't bother with checking the RPM's.
    I took the butterfly (barrel) out of a friend's engine and compared it to mine. The slot machined into the center ring was larger on mine so we tried using his butterfly. Solved the problem instantly. I don't know if mine had a machining error or if the butterfly was from the wrong engine. Suffice it to say it finally runs and idles like a YS. I hope the butterfly is cheap.
    Thanks for your help.
    Phil

  12. #12
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    RE: Badly running YS 63S

    The throttle barrel is $20.50 on Central's website right now.

    Good to know you found the culprit.
    Team YS, Team Airtronics
    Pattern Junkie, Revver Brother #82, Gear Head


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