Vacuum leak?

[danofthejungle]

2008 GS500 naked, 6500 km

So I decided to take my carbs off for the first time a few weeks ago for cleaning.  Apparently, there was no need.  Jets were clean, bowls were spotless.  After that, the bike just seemed to run rough.

Symptoms:
1. rough idle
2. puffing sound every few seconds with a related drop in RPM when warming up
3. more vibrations throughout the bike.  I could feel it at the foot pegs and the handles

Looking it up, it definitely sounded like a vacuum leak.  I took it apart again multiple times to see if I could seat the carbs better.  I got rid of the puffing noise for the most part, but startup always seemed to show the same symptoms (rough idle that seemed to be the same as the vacuum leak, but not as significant.

Made my own sync tool, and synced the carbs, and it seemed to work better w.r.t startup initially, but starting it up again 1 day later, the RPMs would stay at 4-5K RPM (no choke).  Turned the throttle and released, but the RPMs increased and SLOWLY decreased.

Next step: adjust the idle screw.  This brought the idle down to 1200RPM (took quite a few turns!)

However, I could only take it for a test spin another day later.  This revealed a hanging idle - taking off was ok, but once I released the throttle, the RPMs didn't want to drop until I pulled the clutch in.

Thought, "dammit, I thought carbs were relatively easy to do once you got started!"

Decided to take the whole thing apart again and clean the carbs again (maybe the jets were clogged?)

Before I got there, I played with the throttle cable for freeplay (it was in spec already), checked the routing of the choke cable (it seemed to be wrapped around the clutch cable, so I fixed that), and decided to stick my finger into the intake boots.  Feeling around, I felt a small but hard piece of something.  Looked like dirt.  Probably got in there from taking the carbs off the bike so many times trying to figure it out.

Put the bike back together to see if that helped, and it did!  The bike runs smoothly, no hanging idle, no rough idle.  That little bastard seems to have prevented my carbs from getting a good seal! 

Suggestion to anyone doing their carbs:
1. oil or lube the carb boots before seating the carbs onto the engine.  The carbs popped right in much easier.
2. use your finger to make sure there isn't any dirt or particles on the boots to prevent a good seal
3. remove the fuel petcock before taking the airbox off!  It catches on the vacuum hose making it hard to get out
4. use the BaltimoreGS method for removing the fuel tank with the lines attached.  I tried both ways, and his method is WAY easier to get the fuel lines back in place.
5. take a picture before removing the vacuum lines/fuel lines! It will save you the hours of looking information up online/in manual just to try to find the 'proper' routing.
6. If possible, put a hose extension on the vacuum port for syncing!  The later model carbs seem to be impossible to attach the carb sync tool without unseating the carbs from the engine.  (I still have to do this and figure out the best materials to use)

TL;DR: had vacuum problems, felt the inside of the boots and found a small particle that was preventing a proper seal.  Sometimes the strangest issues can have the simplest causes.