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Removal and reinstallation of throttle butterfly

in General Tech Discussion 6 years ago
Is there a knack to the removal and reinstallation of the throttle butterfly valve from a bing 64 carb? It seems an overly tight fit to slide the butterfly valve out through the carb throat (and back in again) without scratching the carb sidewalls. The butterfly is the correct way round (dot facing engine side and on top) I am sliding the butterfly out horizontally in line with throttle shaft.

  • Re: Removal and reinstallation of throttle butterfly

    by » 6 years ago

    It is a tight fit, you just have to be careful. Have you seen the video on Bing 64 disassembly?
    ( http://www.rotax-owner.com/en/videos-topmenu/elearning-videos/309-4carb-dis ) - actually we have a series of videos on that carburetor...
      
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  • Re: Removal and reinstallation of throttle butterfly

    by » 6 years ago

    Thank you for your reply. Yes, I have watched those videos over and over again. The Rotax-owner.com tutorial videos are absolutely fantastic and a brilliant aid to back up the heavy maintenance manual. I can see from the video that it is a tight fit and the valve comes out and goes back in with a little wiggle and a jiggle but in practise it seems to be much tighter.
      
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  • Re: Removal and reinstallation of throttle butterfly

    by » 6 years ago

    Sure! I suppose you could gently warm the body of the carb (to expand the metal ever so slightly) and then try a very carefully directed shot of Freeze Spray, right on the butterfly - to make it contract a little. (Example: https://www.walmart.com/ip/Max-Pro-FR-Blow-Off-Freeze-Spray/21576411 ) Maybe just leave the butterfly in a freezer for a few hours before re-assembly?
      
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  • Re: Removal and reinstallation of throttle butterfly

    by » 6 years ago

    That was going to be my next thing to try as it has been very cold. Did older carbs have a longer distance between the position where the butterfly valve is housed into the throttle shaft and the end of the carb throat and was there any internal step? Having watched the video again (albeit without the carb in front of me to directly compare) it seems a much shorter distance and there is no internal step. The carb in the video is dark matt grey. The carb I am looking at is a light grey/ normal cast aluminium colour. It is also fitted with a carb heat jacket pressed on around the outside of the carb throat. The butterfly valve goes in nicely up to this internal step and then becomes much tighter beyond it. Looking at photos of the outside of the carb I am working on it definitely looks like the throat has been extended to accept the carb heat jacket.
      
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  • Re: Removal and reinstallation of throttle butterfly

    by » 6 years ago

    On another note but on the same carb I noticed that the plunger needle was fitted with an o-ring. On reinstalling a new o-ring and then marrying it up to the plunger needle attachment screw I saw that the needle clip (set on stock position 3) wasn't sitting flush with the the attachment screw housing. Thanks to your videos it appears that this is an older style carb that has at some point been retrofitted with an o-ring but without upgrading the attachment screw with the double stepped and deeper chamfer to accept the O-ring. I am assuming that my correct action should be to not reinstall the O-ring (unless I upgrade the attachment screw) as otherwise the needle will be sitting in a lower position equivalent to having the clip set on a higher and leaner setting say on position 2 rather than 3? Also I can see how it is possible for the needle to be tightened up with the attachment screw and not sit straight in the carb body and therefore needle jet due to the O-ring being in place.
      
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