Things that go 'EXUP'

Checking and fixing the exup Jarmizz style... (thanks for writing this Jarmizz):
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Checking the EXUP valve is easy peeze. Take the left hand fairing off just sitting under the sump casings you will see a strange looking thing in the exhaust thats the EXUP valve take that silver cover off ( i think they are 4mm grub screws but cant rememeber to well) and then you will see where the cables meet up with the exup valve. Turn the engine on and get someone to rev the engine and if the cables move the exup valve then its doing its job. You should also when turning the ignition switch to on before you push the start button hear the servo motor do alittle reset sound thats good to hear. If the exup valve dosnt move pull it out of the exup chamber and spray some CRC or WD40 in the moving parts areas they might be alittle sezied from the carbon build up (take off the cables to remove this obviously). Smack it back to getter give her a turn over if it still dosnt move look at the servo motor. Spray alittle WD40/CRC in the cables and if it still dosnt work take it to your local motorbike repairs.
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I would also like to suggest a few additions:
- when you take off the cables from the valve turn on/off the bike. The servo motor should move at this point. If not the servo is dead - go to a wreckers and get one is the best option (it could actually also be electrics in this case, so you may want to check there but that is a whole new can of worms so I won't bother discussing here). It is very unlikely that the servo is dead though.
- if you end up taking the exup valve out of the chamber (which can take some effort and perhaps some hammering but it will come out just so you know...) clean it with a wire brush or something else because the carbon may not all come off with crc/wd40. (the valve itself is not fragile, so you don't have to be super gentle with it). Even if it seems to move freely when you play with it by hand it may still be a little tight, so remove it and clean it anyways.
- the exup valve->servo cables should have virtually no slack in them. To tighten you 'loosen' the nuts up towards the servo motor (you will see an adjuster on each cable).
- when adjusting the valve - take an allan key and put it between the 'tooth' on the valve and the hole in the exhaust (you will see what I mean when you look). This is where the exup should be adjusted to according to yamaha specs.

Having said that - I actually have my exup valve adjusted so it is slightly open at rest (the tooth is slightly up from where yamaha states). I have done this because of the problem you have experienced AND I know my engine is running very slightly rich, and this has helped stop my stalling. (I've been busy and not gotten around to adjusting the carbies)

Other things i have found to work/help, if above doesn't solve the problem
1) I have previously unnattached the exup valve (left the cables hanging), and wired the valve so it is open 100% of the time. This stops all stalling, but really degrades bike performance so it is not a recommended solution, but it does work.
2) This is my guideline for city riding that I use (I personally ride the bike in the city between 8000-9500 and follow this guideline)... As you are riding, every once and a while (perhaps every 30 seconds or minute when you are going at a relatively constant speed) - pull the clutch in and rev to about 12-14 000 or so for a second, then let it back down. This will release the back pressure (remember under at 9000 revs the valve is only slightly open, and if your engine is running slightly rich you may not be letting out enough exhaust for how the engine is tuned). This will set you back to normal. Sometimes I will hear a slight dip in the revs, but then they come back to normal - when I hear a dip I often will do this twice in succession and never hear the dip the second time round. Since you are moving the bike actually wants to rev, so it will 'work through' the back pressure issue without stalling. I also rev it the odd time when sitting at lights (this will clear out backpressure again but usually sitting at idle won't be an issue with backpressure. But it can also check to ensure that you won't stall when the light turns green which can be an issue if you have cars ready to move behind you).

 

EXUP - Quick Check

To quickly check to see if the EXUP valve is the source of problems on your bike you can 'wire' it open. This essentially removes one potential problem source, and if your problems go away you can essentially say that something about the exup valve is causing the problems. Note: this may be an interaction with other aspects of the motor - such as running rich.

To wire the exup valve open (you can find the valve under the stand on the left side, below a metal plate). Unhook the cables - leave them dangling for now (you can find a permanent solution if required), and turn the valve clockwise until it won't go further. Wire this in place however you can (I have used some spare copper wire in the past). then try out the bike.

 

this link was posted on the exup brotherhood - a website with a step by step exup adjustment procedure, complete with pics:
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