Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: Towsejames on July 26, 2026, 05:29:39 PM
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Hi again,
Just a quick one. So I’ve recently rebuilt a set of 069a carbs following the video that classic octane posted. All is well and the bike runs nice and smooth, I bench synced the carbs using a drill bit to level each slide to each other.
However I was wondering on the idle adjustment when this was being done. I adjusted this with the idle screw backed right off. Nothing was mentioned in the video about this but now when starting the bike it idles from cold after choke is turned off at around 1200 rpm but doesn’t go any lower once the idle screw is backed right off. As the slides have been set to the size of the drill bit I used with the idle screw backed out.
Was I supposed to keep a small amount of adjustment left on the idle screw to allow for adjustment in lowering the idle - is the bike meant to shut off with the idle screw backed out the full way, ie closing the slides.
Thanks for any advice.
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You have made the most common mistake during a bench sync
1 undo the tickover screw all the way
2pick one carb(any carb as they all have adjusters)
3 loosen the single carb adjuster till the slide bottoms onto the body and lock the adjuster
4 using anew drill shank no bigger than1/16 or 1.5mm screw in the idle adjuster till the drill shank just fits
5 now adjust the other 3 all the same
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I prefer to manually sync them by loosening off the idle screw so it’s not touching. Now set all the slides so they just start to lift, as small a gap as possible. Now adjust the idle screw until they just start to move, check they all look just the same. Fit and then adjust the idle screw when the engines running.
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I followed Kens advice on my 500, if I fully undo the knurled idle screw it stops the engine running.
I adjusted my sliders so they were just about to lift, downside was I had to build up the stop plate as the screw was almost out of the bracket.
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If you use a vac gauge after, you can lift the slides to suit the idle screw, I do it that way so there is no chance of throttle hang afterwards. So long as all the carbs are equal and the idle is around 1000 it doesn’t really matter what number the needles on the vac gauges end up at.
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I prefer to manually sync them by loosening off the idle screw so it’s not touching. Now set all the slides so they just start to lift, as small a gap as possible. Now adjust the idle screw until they just start to move, check they all look just the same. Fit and then adjust the idle screw when the engines running.
I like the sound of this method. Thank you I’ll pop the carbs off again and set them like this.
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We all have different approaches to how we do these things. Mines no better or worse than anyone elses, I just find it works for me and I’ve never had the hanging throttle problem after using that method. If it works for you that’s great. Happy to help.