Infuriating Idle

[SuzukiOnly]

The search function has made this forum incredibly useful, even without actually registering, but I've exhausted my patience for searching and for tuning this motorcycle. It's a 97 with about 20k miles.

In attempting to get it running as close to perfect as possible, I've done the following:
Rebuilt carbs (thoroughly cleaned, new gaskets)
Rejet to 127.5/40
Replaced intake o-rings
Pilot screws 2.5 turns out
Float height set to fuel level at the float bowl gasket
Carbs synched (albeit not precisely)

I've pretty much completely restored this bike, and for the most part it runs and rides wonderfully. But I can't figure out why it does what it does. Once it's warmed up, if the rpms get up to 4k in nuetral, it will hang like I have a vacuum leak. It idles way too low cold, but the choke seems to only function as on or off, only 4.5k rpms or about to stall.

Warm, it will idle at 800-1000 well enough, but if I set it to about 1200, it will climb very slowly to 2.5k or so. But with the idle set at 800-1000, I can blip the throttle and it will settle back down at a reasonable pace.

Not a huge problem, obviously. I still ride every day, but it's really annoying having to hold the throttle to keep it running while cold, and still dealing with what seems like vacuum leaks - despite a starter fluid test revealing nothing.

Any ideas?

[Janx101]

Do the revs vary while idling if you turn the bars at all?

If so you may have a throttle cable issue. . In my case it was making that big adjustable cable tie under the tank (that goes around the throttle/clutch cables) too tight over the cross frame pipe

[floatingLomas]

Did you set the mixture and idle when the bike was cold or warm?

Mine used to do that until I let it warm up fully and then set the mixture and idle.  Now it runs right.

[MeeLee]

Idle to 4k rpm could be carbs that are not in sync.
Get something like this, and sync your carbs with it:
http://www.amazon.com/gp/product/B004MSJ7C8

When the jets are cleaned it could be just the adjustment screw.
Sometimes when one of the two idle jets is clogged, it tends to do the same, and people adjust the screw to avoid the issue, making the idle ok, but when riding one cylinder will work harder than the other.

[BikerMedic]

Id try carb sync.

[SuzukiOnly]

It's not the throttle cable, and I set the mixture screws and idle warm. I think I need a more precise carb sync, so I bought the valve and Ts according to the gstwins $5 carb sync tutorial. Does it matter if its cold or warm for a card sync? What are the most common vacuum leak locations?

[MeeLee]

without having the bike in front of me, each carb supposed to have a vacuum connection on the top of it (facing the seat, and at the corner of the carb towards the fuel tank facing upwards; either plugged with a rubber cap, or a hose).

Carb sync must be done warm, or else you'd be measuring the vacuum on the choke if you use it.

It should be measured while idling and revving, to see if any jet is clogged.
Usually 4k rpm is idle jet clogged, but other jets should be checked as well.