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bs34 cv carb slides getting stuck at top

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

Guest
Hi

I just fitted new diaphragms to the carbs on my gs1000g. I tested them by pushing the slide all the way up and seeing how the slide came down. The all seemed to return reasonably slowly but one of them seems to get stuck at the top, from 3/4 to the bottom it seems to be ok though. Any ideas what could be causing this, weak spring? Maybe with the new diaphragms stronger springs are needed.

Cheers

Dave
 
Try switching the suspect slide to another carb and see if it it sticks in that one.
 
The slide on its own slides down fine, I think it is just the new diaphragms are thicker and therefore less elastic than the old ones, probably they will get better with time. It seems anyway that the slides dont reach the top in normal usage as shown in this video.

https://www.youtube.com/watch?v=tR63vrfhwr8

Just one question, is it just the spring that pushes the slide back down, or is it also helped by pressure at all, just that the slow speed that the carb slides return (eg. when released using a finger) would make the engine not back off the power immediately?
 
The underside of diaphragm "sees" the airbox pressure at all times thru that beanie shaped slot- atmospheric at idle ,but drops off as carbs start swallowing lots of air. Acts as a "cushion" to sudden changes in slide movement
 
I swapped the slides and spring around a bit and they are all falling fine now. This is just the kind of thing that will drive you mad when balancing the carbs, glad I sorted it out now
 
DaveWatts said:
Just one question, is it just the spring that pushes the slide back down, or is it also helped by pressure at all, just that the slow speed that the carb slides return (eg. when released using a finger) would make the engine not back off the power immediately?
Click to expand...
Gravity is usually available to help the spring. And there will be no problem with the engine backing off the power, because it's not the slide that is controlling the power, it's the butterfly just downstream of it. When that butterfly closes, the engine is getting NO air, so power stops NOW.

I thought the video was going to be of your bike, but that is not what I saw.

DaveWatts said:
I swapped the slides and spring around a bit and they are all falling fine now. This is just the kind of thing that will drive you mad when balancing the carbs, glad I sorted it out now
Click to expand...
How would this drive you mad when balancing the carbs? How would you notice? You would usually have the airbox or the pods installed, so could not see the slides. :-k

.
 
Steve said:
Gravity is usually available to help the spring. And there will be no problem with the engine backing off the power, because it's not the slide that is controlling the power, it's the butterfly just downstream of it. When that butterfly closes, the engine is getting NO air, so power stops NOW.

I thought the video was going to be of your bike, but that is not what I saw.

How would this drive you mad when balancing the carbs? How would you notice? You would usually have the airbox or the pods installed, so could not see the slides. :-k

.
Click to expand...

Your right, I didn't think about the butterfly. But doesn't the butterfly say 'now stop giving me power', but the slide is slow and when it opens again it has too much fuel for the butterfly, they have to sync right?

About the balancing - You would try to balance the carbs but fail to do it because there was another problem namely the slide not rising the same as the others no matter how much the linkage is adjusted, you wouldn't see this with the airbox on which would make it even more difficult to diagnose.

I hope to take a better picture of my bike when it stops raining, its the end of April and its still cold and wet!
 
DaveWatts said:
But doesn't the butterfly say 'now stop giving me power', but the slide is slow and when it opens again it has too much fuel for the butterfly, they have to sync right?
Click to expand...
There is no mechanical synchronization between the butterfly and the slide. The slide lifts because of the vacuum caused in the venturi. The vacuum is caused because of air flowing, the air flowing is caused by the open butterflies. If the slide sticks or there is a hole in the diaphragm, it will not respond as quickly, but the slide never "has too much fuel for the butterfly".


DaveWatts said:
You would try to balance the carbs but fail to do it because there was another problem namely the slide not rising the same as the others no matter how much the linkage is adjusted, you wouldn't see this with the airbox on which would make it even more difficult to diagnose.
Click to expand...
At the engine speeds and throttle settings used during a carb sync, you would not even see the slides move. :-k
They don't open until there is sufficient airflow under them, that does not happen until at least half throttle. You might see them lift a bit when blipping the throttle, but not during a normal carb sync procedure.

.
 
Just to clear up (I shouldn't post under the influence of a cold), I don't mean a mechanical synchronisation only that they work together (the physical connection being the movement of air & air pressure). I also shouldn't have said "slide not rising the same" but the synchronisation mercury raising the same and that with the airbox on you can't see the slides to see that the problem was really with the diaphragm not the throttle screw adjustment.

Cheers

Dave
 
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