Trying to work out why one slide is sticky at the bottom of its travel. After lots of swapping parts in and out, including parts from an old carb, it turns out that the aperture in the throttle slide is slightly too tight for the choke slide to run smoothly between jet block and throttle slide. I seem to remember some comments that new anodised throttle slides might be better than chromed ones? I had chrome slides on Concentrics with no problems.
Now to take a little off the thickness of the choke slide and try again.
Finally sorted it out. The…
Finally sorted it out. The slide fits properly. But there were two issues which added up to confusion. The air slide was a couple of thou too thick to be an easy fit between jet block and throttle slide. Cured that using a flat file. But it was still a bit sticky. So after more inspection I used a small flat file to smooth the slot in the jet block (the one that guides the throttle slide) and now its free to move properly.
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Good it's sorted David! For…
Good it's sorted David!
For future reference, if someone comes across this topic, I'd like to add that sometimes the jet block can be misaligned (rotated). This happens when the fixating screw has at one point worked loose, with vibrations causing it to widen the slot in the jet block.
When you remove the block for cleaning and place it back, normally, the fixating screw stops it from rotating, but as there's now play in the slot where the screw fits into, the block will rotate slightly when you tighten the jet up.
You can't tighten the fixating screw enough to prevent this, but carefully gripping the inside of the jet block with parallel pliers (covered in cloth), helps you to align the jet block.
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One other thing...
... it's possible that the jet block can have been distorted if it's been fitted in a ham-handed manner. They can be a bit tight in the carb body and some people just whack them in - they're quite weak round the waisted portion.
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Thanks Ian - but it's a new…
Thanks Ian - but it's a new carb and the jet bock slips in and out easily. But it's working fine now after I filed the air slide.
Although I still have a slight issue. When it's on tickover at traffic lights, the revs rise steadily over a minute or two towards 1500 rpm or more. If I blip the throttle, revs fall back again. I'd better check for air leaks at the joints, but it does seem odd. The bike otherwise runs well right across the range.
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Unusual for the choke slide to stick, they are a very loose fit in the jet block and slide. (There is a very good tool room expression for the fit, best not repeated here!).
Have you removed the jet block? Its easy to distort removing/installing. Might that be causing the sticking?