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  1. #1
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    Trx 3.3 needs large carb opening to idle

    I have a revo with a trx 3.3 I bought used. I had to replace the clutch/clutch spring, engine case with bearings, and I put a buku case cap. The truck is fast and running well except I need to screw the idle screw all the way in before it'll idle. Even then, I have to trim the throttle to open the slide a bit more to keep it idling. Anyone experiencing this problem?

    When I hit the brake, the throttle gets pushed further in which kills the motor.

  2. #2
    RC Turnbuckle Jr. icepick832's Avatar
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    Have you checked the gap in the carb slide? To me it sounds like your LSN is out of tune and your compensating for it with the idle adjustment. There should be a 1 mm gap in the idle slide when not giving brake or throttle input.
    Here's a link to factory settings.
    http://traxxas.com/support/Factory-C...-25-25R-and-33
    Here's a tuning link.
    http://traxxas.com/support/Tuning-Yo...-Performance-0

  3. #3
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    Quote Originally Posted by icepick832 View Post
    Have you checked the gap in the carb slide? To me it sounds like your LSN is out of tune and your compensating for it with the idle adjustment. There should be a 1 mm gap in the idle slide when not giving brake or throttle input.
    Here's a link to factory settings.
    http://traxxas.com/support/Factory-C...-25-25R-and-33
    Here's a tuning link.
    http://traxxas.com/support/Tuning-Yo...-Performance-0
    Thanks. I will try the lsn settings tomorrow. It seems to be too rich overall, since I'm down to 3 turns from closed on hsn and much lower than the 2.5 or "flush" with the inner ring with the lsn.

    I assume leaning out the lsn should make the idle raise up correct?

  4. #4
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    Yes, the LSN is approximately 2 turns out from the stop, and that should make the screw flush with the ring.


    Sent from my Nexus 4 using Tapatalk

  5. #5
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    I'll give that a shot

  6. #6
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    I took apart the carb and inspected the needle, all seems ok. This carb was recently rebuilt with a new carb body and all new seals. The lsn has zero effect on the idle, even when it was bottomed out. The car runs with the lsn bottomed out and there's fuel spurting out of the throttle body, any ideas as to what's wrong?

  7. #7
    RC Turnbuckle Jr. Snook Man's Avatar
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    Check the piston orientation before you go any farther, those are all classic signs its installed backwards.
    No slipper/tall gearing/power = broken parts.

  8. #8
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    +1, try the piston.

    Sent from my Nexus 4 using Tapatalk

  9. #9
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    Best way to check the orientation?

  10. #10
    RC Competitor
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    Engine out strip it down and rebuild. There is a guide on the traxxas site on how to check orientation.
    Hopefully someone can post a link for you.


    Sent from my Nexus 4 using Tapatalk

  11. #11
    RC Turnbuckle Jr. Snook Man's Avatar
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    Remove header...Piston @ TDC when looking into the exhaust port you should not be able to see the con rod. If you can, its backwards.
    No slipper/tall gearing/power = broken parts.

  12. #12
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    Okay sure enough the piston was backwards. I flipped it and reassembled, now it's running like a champ. Only took a new crankcase w/bearings, crank cap, carb seals, carb body, and lots of time! Thanks snook man and all for your help!

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