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Question for the Carb Experts

Nessism

Nessism

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Just finished rebuilding the CV carbs on my 1981 GS550T. The carbs are low mileage but sat with for a long time so the O-rings were hard and cracked and the jets were gunked up.

When lifting the slides with my finger, three out of four have a nice smooth damped movement both up and down. One slide though does not have this same consistent damped motion - there is dead spot so to speak where the the slide moves freely - not damped. I removed this slide and put it into another carb body and the issue follows the slide. I've inspected the diaphragm closely and it is not torn or damaged in any way. The slides are all in perfect shape with clean, smooth anodizing so I know the slide is not worn at all. Carb bodies are clean as well.

Does anyone know whether or not this is a problem and if so, how to fix it?

Thanks.
 
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It doesn't sound right to me. The answer you don't want to hear is replace the slide. If you have an air compressor, you can lightly blow air into the air inlet located on the air cleaner slide of the carb and watch the movement of the slide and compare it to the other ones.
Does this odd movement happen as the slide is going up, down or both ways. Have you tried a different spring?
 
Gotta be the spring or the diaphragm...

I second the motion to try swapping the springs around and see if the problem follows that spring.
 
By all means swap them around.

Sounds like a leaking diaphragm.

Is it fitted correctly?

The diaphragms have fitting tabs on the outer edge, and if one is raised a bit due to not being positioned correctly in its slot, you may be getting an air leak because of that.
 
Take out the slide and check for pinholes in the diaphragm with a bright light behind it. I had the same problem once and the slide spring wasn't in the cap properly.
 
Check very closely at the point where the diaphragm flexes at the top outer edge...sounds like a tiny crack that opens up and closes based on the slide position.:idea:
 
Thanks for the input. The glitch in the slide movement occurs after the slide lifts off the stop - maybe from 5mm - 15 mm open. It occurs when moving in both directions. I'll pull the slide again and use a light behind the diaphram to look for a crack. One question: what creates the damping action for the slide? Must be the some sort of restricted airflow of somewhere.
 
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You can raise the slides manually by sucking on the upper portion of the airbox side of the carbs.:-\"
 
If you remove the slide and look where the needle projects, on the underside of the slide, there is a small hole, this is the "vent" you are looking for.
I would try swapping the springs around and see if the "pause" follows the spring or the slide.

Dink

Edit: check if the "vent" holes are clear.
 
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Okay, checked the diapharam again, this time by filling it with water! No leaks!

DSC01946.jpg


Vent hole is fine also; consistant with the others. Going to try swapping around springs now.

EDIT: moving springs does nothing. I'm starting to thing this situation is normal. If I lift the slide slowly it will move smoothly. If I lift quickly, the slide still has that dead spot as described - the others don't. For lack of anything else to try, I'm going to try running the bike as is unless someone can suggest something else.
 
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