Hung idle issue - Monster 400 200

[ZachMercer]

Hello All.

So I'm looking for anyone's thoughts and suggestions on a hung throttle issue I'm tying to work through on my 2000 Monster 400.

What's happening:

Bike starts (with choke) without a problem, and I can get it to idle at 1200rpm after a minute or two. I back the choke off and it will maintain idle for about a minute, then it climbs and hangs at 3000rpm. Nothing will lower the revs other than shutting.

It should also be noted that when at 1200rpm, if I give it a bit of throttle, it will also jump to 3000rpm and not come back down.

What I've done:

* Checked around the carbs (Mikuni BDST38's), airbox and manifold boots, vacuum lines, vacuum nipples, etc with carb cleaner spray to find a vacuum leak. I can't find anything that drops rpm.
* Removed carbs and checked bowl heights, cleaned all pilots and channels, diaphragms aeated correctly with no tears or holes, etc.
* Replaced all vacuum lines given its age.
* Set and tested mix screws to 2, 2.5, 3 turns out to gauge lean and rich.
* Set warm idle to 1200 before jump in rpm.
* Synchronised the carbs with vacuum gauges.
* Replaced a pinched fuel vent hose.
* Checked for any obvious leaks around the airbox.
* Checked the throttle cable tensions and that the plate was snapping shut. From what I can tell nothing is binding, and rpm doesn't shift when turning the bars.
* Check the choke cable tension and operation.
* I removed a gear indicator that was pulling a pulse from one of the spark plug cables.
* Made sure that at the airbox and the manifold that the carbs are sitting flush and without over tightened hose clamps.

My thoughts:

It's getting extra air from somewhere. Everything points to a vacuum leak as it's jumping and hanging when warmed up. Either that or something within the carb is worn or failing, or I'm running the bike much leaner than 3 turns and it needs to be out more?

Could it be something electrical? Or something else I haven't looked at.

Any thoughts or advice would be great, before I have to arrange for it to be taken to a Ducati shop.

My best, and thanks in advance.

[koko64]

Warm the bike up and check the idle speed again. If it idles high again back it off to about 1200 rpm. Let it cool right down and and come back in a few hours to test again.

Try this before doing other stuff, just in case the bike wasn't quite hot enough when you set the idle.