tarted diagnosing high/runaway idle this afternoon. At first I thought it was a fuel delivery issue, but got the petcock to perform as normal. Then tried to start things up and it cranked for like 30 seconds with nothing doing. Tried this four or five times. sixth time, it starts to bobble. Seventh time, it fires and I get the high idle. What's building, the pressure? Vacuum in the fuel delivery? Why does it take so long to start up? Yes, this happens every time I start the bike.

1. Replaced the intake boots, o-rings, and cleaned the carbs.
2. Did a valve adjustment. It's possible the exhaust side are still slightly out of tolerance on the loose side.

3. And here's the vacuum part: Got it running at normal idle. Give it some gas and the revs go up, and SLOWLY come back down. I notice the vacuum port for the petcock is open. Oops. Cover it with my finger, give it some gas and it revs up....and stays up. Let my finger off the vacuum port and it slowly comes back down. What's going on here?

Carb gurus I need you!

OK. So runs, but fuel starved. Fuel petcock ok.
What about a partial vacuum developing in the tank? There is a tiny vent hole in the edge of the fuel tank cap. This lets air into the tank so fuel can come out. If no air can get into the tank (or gets in very slowly) then you get a partial vacuum inside the tank and fuel won't flow out. The more full (i.e. fuller) the tank, the less air is in there to expand as you pull fuel out. So a full tank will be more susceptible to this than an empty tank (its just the physics of air expanding)

Try it with the fuel cap open (at least not locked closed) and do you have the same problems? It can be the fuel screen inside the tank is all farkled up. I've got spares. Look down in with a flashlight. How does the filter/screen inside the tank look? If crappy, I can bring you a good one. Only a couple minutes to change out (minus time to empty the tank and refill it).

Is the throttle sticking? Is the choke on or off?

Drain carbs, could be junk in idle jet and this might fix it if you're lucky (I was).

Did that.  Twice just to be sure.  There is a bunch of sediment coming from the tank still, but it's getting trapped by the inline filter.  I know I do need to clean the tank out.  Any suggestions on how to get all the rusty sediment out of the tank? 

Well  use a temporary fuel supply to check how it runs after you clean the carbs again (In case you have more crap stuck in the carbs from  the sediment.).Universal  radiator overflow kits from advanced/autozone work well. 
http://gstwins.com/gsboard/index.php?topic=4282.0

Did you make sure you put the small orings back in the carb tops (yes I know it says you replaced orings...)-they can be  displaced easily while working on them..?
Did you fool with the idle adjuster under/between the carbs trying to get it to run?

The best thing you can do for your tank is a POR-15 kit ( cleans and seals the tank to fix and prevent rusting further).

Quote from: scottychop on March 26, 2011, 08:11:37 AM
Did that.  Twice just to be sure.  There is a bunch of sediment coming from the tank still, but it's getting trapped by the inline filter.  I know I do need to clean the tank out.  Any suggestions on how to get all the rusty sediment out of the tank? 

Is it an automotive filter?

Nope.

WTF!  The PO had obviously done some "work" to the carbs as mentioned in my broken choke stop thread.  Well, the PO strikes again!  No orings - quickly remedied.  Went to loosen the rubber cap up top, and the whole nipple cracked off in my hand.  Geez!!  We need to start a thread about PO mistakes....... hmm.....

Might want to source out a set of carbs in the near future... might be able to epoxy the nipple closed at least to get it to run.

California set on Ebay for about 40$ at the moment...