Up to her old tricks again

[JV]

She's at it again!

Alright, so I used the pegs today, and didn't crunch my nuts.  
Unfortunately, after about 10 miles she ('96 600S) wouldn't idle much.  Very low idle in fact.  So I brought the bike home and tried to start it in the driveway.  No such luck.

My initial thought is to just crank up the idle, but that's just chasing the symptoms instead of the problem.  So what's the problem?!

Thanks,
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[chupacabra]

Drain your float bowls checking to see if all four have gas in them, maybe a stuck needle valve. What I do is use a clear hose (hook it to the drain outlet) and run it straight up so you can see what the fuel level is in each bowl.

Check for a vacuum leak.

Check your plugs (see if all four look the same)

I'm betting on a vacuum leak

[tacoman]

I'm with the vacuum leak theory.  I had a gixxer 1100 that had a fuel petcock go bad and leaked vacuum.  Being the carbs work off a diaphragm, vacuum problems can cause all kinds of woes.  Check all your vacuum lines, try running the bike on reserve to see if there's any change, maybe even pull the petcock out to see if the tiny filter screen has clogged.

[JV]

Thanks for the replies.

I got 1.6 miles today before it happened again!

I looked in my Haynes manual, but all their carb stuff is done off of the bike.  How do I drain the float bowls?  (Sorry, I'm a carb virgin.)

I've checked the Petcock, perfect condition.  I'm checking the plugs today.

I did discover one thing.  After it died in the middle of the street, I could run if I waited a second.  I could also ride around with the petcock in PRI and the choke on.  

When I got home I cut the choke and turned the fuel back to the ON position.  It idled fine.  WTF!
If I gave it a quick rev up to 4-8k it would idle down to 2k rpm.  It would hold there for 5, 10, even a count of over 15 seconds.  Finally it would come back to a wavering idle around 1300 rpm.

Riding home in PRI w/ the choke on was quite fun w/ all the extra torque.
  [/img]

[tacoman]

My gixxer did the same thing.  Its vacuum.  Two things it can be.  A faulty petcock letting air in or, if the vacuum lines are ok, carb problems.  They can be dirty, malfunctioning, or both.  If you can only run with prime on and a choke, thats a lot of fuel.  Try looking at the diaphragm for damage, pinched bladder, etc.

[JV]

So, um, how do I check for vacuum leaks?  If I check the Petcock vacuum, then how do I get fuel into the bike?  Der, um, I'm retarded.

[PeteSC]

Isn't there some trick involving spraying water or windex....some fine mist...at the vacumn lines while the engine is running, and listening for a change in the sound of the engine?  
  (Back in the recesses of my crossthreaders brain lurks something....)

[Red01]

I prefer to use starting fluid or propane. Water may not give you enough rpm change to tell.

[JV]

Okay, I tried squirting WD-40.  No luck.  I did the petcock and associated vacuum line and I did the top covers of the carbs.  Where else should I be squirting?

How much rpm change should I see?
Also, my idle wavers.

While doing this I did notice one thing.  After the engine was hot and then ran about 10 more minutes, it would idle w/o choke, and it dropped from 1200-1300 rpm to ~1000 rpm.
WTF?

Any quick throttle changes try to kill the engine.  
Could this be an ignition problem?

While listening and spraying, it became obvious that I need to adjust the valves, too.  
I also noticed the other day that the first cylinder burns oil.

I'm ready to replace my Bandit.

[Red01]

Someone pipe in if the 600 is different, but on the B12, the idle should be ~1200rpm when the engine is good and warm, so if you're idling at 1000 with it warm and the choke off, you're too low.

[Red01]

If it still tries to die with quick throttle with the idle turned up, you're either too rich or you have a vacuum leak. In addition to what you've already checked, spray the carbs them selves and the manifolds between the carbs and the head.

If you use a combustible, RPM will increase when you find a leak.

[JV]

I found a huge leak!!!

The diaphragm that controls the #4 jet needle had a major tear!  It was from the previous owner (AGAIN!) being a ham-fisted mechanic.

I ordered a replacement and fixed the tear a bit w/ some super glue.  (Had to try and ride on the 4th.)  Unfortunately, this didn't fix the problem.

Guess I'll wait for the parts!

[JV]

Friggin eh!
New diaphragm/piston didn't change anything!  

Could it be the jetting?  Mixture adjustment?  How can I tell?

[JV]

Hopefully this time I won't be the only one to answer my own posts...  

So my neighbor that has owned ~10 bikes and teaches MSF courses gave it a look.
He thinks it could be a couple things.  Varnished carbs (from not draining the bowls in the winter   )
And/OR the synchronization.  
Does this sound right?

How should I, a carb virgin, go about cleaning them?
The local place wants $430 to do it!

[NCBANDIT]

I'm sure someone else will correct me, as i'm a street carb virgin. But on all my dirt bikes I removed the carb(s) and removed the float bowls and slides, the spray liberally with carb cleaner( i would buy a small fine bristle frush to help break up the varnish). Then remove the jets and hold them up to light and or run a fine piece of wire through them to check for obstructions, then spray with carb cleaner. Also check where the jets screw in and and clean the needle and seat area. Be sure to check the floats and make sure they are not cracked ( shake them and see if there is gas inside), no one has said it as you didn't mention excessive smoke, but you could have a sunken float (going out on a limb here) Hope this helps some, Josh