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30.5cc what carb?

Discussion in 'Large Scale RC' started by Jacedia, Jun 21, 2014.

  1. Jacedia

    Jacedia New Member

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    Running a cy 30.5cc big bore kit on my losi 5ive T stock carb believe its a walbro 668, had nothing but a nightmare getting it running right get it to idle but acceleration is trash get decent acceleration and wont idle at all, if i change low speed needle at all to run right at top speed just overheats pn me and the killer bee cuts it off, would i be better to upgrade to a walbro 813 or 990 carb would it solve the issues im having? Been running a 5b for a long time with a 26cc zen in it never had such trouble dialing it in before
     
  2. TeK

    TeK the 1/5th Scale BOSS
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    Unless you have a bad carb ie it's got dirt in it, it's not your issue. A 668 is fine with the motor you have. I would not recommend an 813. A 990 is also good but you won't notice a difference over the 668. The killer bee does not cut off for heat, only for low voltage or a radio glitch like loss of signal.

    What are your needles set too?
    Have you broke in the new cylinder yet?
     
  3. Jacedia

    Jacedia New Member

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    Yeah did break in with a bunch of issues with keeping it running, been reading up a bit more on it and im thinking maybe squish clearances never checked that when i put it together but carb looks clean when i took it apart and ive went back to stock needle settings for now to try to get a baseline again
     
  4. Jacedia

    Jacedia New Member

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    I live in fernie bc should just bring it up to calgary and pay ya a visit everett lol
     
  5. mickyd213

    mickyd213 Studio Forums Elite
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    By the sounds of it the motor is running but won't stay running so I'd adjust the idle screw. It's on the opposite side to where the throttle linkage connects to.

    But there are a few checks you can do...

    Check fuel mix...
    Check your coil gap... Usually around a business card thickness.
    Spark plug... What colour is the electrode, it should be a light brown colour which indicates it's tuned ok.
    Hi and low speed needle settings... Ties in with spark plug colour... You can run it rich but it may cause fouling down the track... Factory settings on the 668 carb is 1 1/4 turns on the low speed needle and 1 1/2 on the high speed needle ccw (From fully closed) Don't overtighten the needles when closing it off.
    Adjust the idle screw and throttle linkage.
    Check for air leaks around the carbie.
    Check for leaks around the head. Maybe the head bolts aren't tightened enough.
    You might also need to check the ring to make sure the bore of the engine isn't damaged...

    You can check squish with the motor still fitted to the car. Just use a piece of solder and it will give you a good indication. Bend the end into an "L" shape so it can get to the cylinder wall and turn motor over slowly to squash the solder. A set of verniers is needed to measure the squish. Anything from 1.0mm down to 0.3mm is ok... You can go less if you want but these measurements are a guide only.
     
  6. Jacedia

    Jacedia New Member

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    Turned out to be a small tear in carb gasket new gasket little bit of tuning in the stand and shes running great thanks for the tips guys love everyone of ya on this forum
     

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