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vacuum release on carb diaphragms

  • Thread starter Thread starter matt_gs450
  • Start date Start date
M

matt_gs450

Guest
Hi All,

I recently rebuilt the carbs for my 82 gs450, and noticed that the left carb body would release the vacuum around the diaphragm more quickly than the right carb (tested with the carbs off). The right side would hold the vacuum for more than 15 seconds before the slide started to lower. The left side would only hold the vacuum for about six seconds.

I swapped the diaphragms to see if that was the cause. It wasn't.

I noticed that the mating surface between the diaphragm and carb body was not as smooth on the left side as the right. The left body had sort of a texture while the right body was very smooth. I assume this is what is causing the vacuum to release.

Is this by design? Or did someone swap out a carb body on this bike somehwere along the way and leave me with a mismatch?

I went for my first long ride yesterday and while the overall performance was very good, the power would drop at times causing me to throttle up. I imagined it was re-opening the venturi on the left carb by doing so. On the other hand it was very windy (30 mph gusts) and perhaps the changing air pressure was altering the mixture on the fly and causing it. Any thoughts?
 
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I see that your bike is an 82 GS450 so I'm assuming they are CV carbs. I'm sure I will be corrected if I'm wrong but I don't think either of them should stay open at all once the vacuum is released. I've rebuilt several different sets of CV style carbs and once I was done cleaning them they started to close immediately once the vacuum was released. They would take a couple of seconds to get to the fully closed position but didn't 'hang' full open at all.

Anyone disagree?

Pete
 
Hey Pete. Sorry, I didn't clearly state what my test was:
1. push the diaphragm up to the fully open position (against the spring) simulating vacuum
2. block the vacuum port with my thumb
3. time how long until the diaphragm returns to the closed position

Both sides would return to fully closed just fine if I didn't block the vacuum port.
 
Sorry for the confusion. The orifice I blocked (and was referring to as the vacuum port) is on the airbox side of the carb, on the diameter of the bore. It's actually not a vacuum port. It is connected to the cavity on the underside of the diaphragm and helps to push up the slide with air coming in through the airbox.

The vacuum is admitted through a small hole in the slide itself.

In any case, plugging the orifice on the bore can test whether there is an air leak in this system.
 
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