1982 GS1100GK - One of the carb slides just drops

[MtnManCA]

Hello,

I have been experiencing occasional hesitation during acceleration with my 1982 GS1100GK. 99% of the time the bike runs very well and accelerates hard (also starts and idles very well) but once or twice during almost every ride the bike stutters and hesitates. Seconds later it runs normal again.

Whacking the throttle wide open seem to help, so I thought this issue might be vacuum related. Today I removed the air box and found that the slide of carburetor 1 just drops after lifting it up with a finger. The three other slides slowly drop with a sucking noise.

I checked all 4 diaphragms and slides for any damage but couldn’t see any. No holes or tears in the diaphragms and both the slides and carburetor barrels are clean and smooth. I also made sure that the diaphragms are sitting correctly in the groove.

Before I order a diaphragm from CMSNL for $167 I need to understand if anything else could cause this.
What do you think?

[MtnManCA]

As soon as I posted this it occurred to me to swap slides. I installed the suspicious slide in carburetor 4 and it dropped quickly like it did in carburetor 1. I also installed the “good” slide of carburetor 4 in carburetor 1 and it dropped slowly with a sucking noise.

I will order a new diaphragm.

[chuck hahn]

backlight the diapram with a flashlight and look for pinholes of light.

[MtnManCA]

backlight the diapram with a flashlight and look for pinholes of light.

That’s what I did, twice! I didn’t see any hole or tear.

I still have a hard time to believe that the bike ran - mostly - so well! Very eager to see how it runs with an intact diaphragm