God I hate Mikuni carbs (on 4-strokes). I swear, if it wasn't for Blair's (Litetek) knowledge & kits and the help of this forum, I'd never buy a mikuni-carbed suzuki or yamaha ever again. I have a set of Mikunis (BST29) off a 1999 Suzuki Bandit that I have to rebuild. They unfortunately leak like a sieve and, as I have discovered, there are quite a few issues needing resolution. Before I start, who designs these things? Do they hand out paper and crayons at the local pre-school centre and then take whatever's drawn and try to make a carby from it? Seriously, I've never seen so many orifices, jets and passages that not only do nothing, they're almost added on to confuse the person working on them! "Oh crap, we forgot the *** circuit." "Don't worry, we'll just run a copper pipe from the top to the bottom of the carb. No-one will notice." Give me a set of Keihins any day. Anyway, on with the story. I tend to break carbs down to their basic parts, so I can clean them properly as well as discover what else might be wrong with them and what needs to be replaced. The only thing I don't do is remove the throttle blade and replace the shaft washers etc. I do check how much the blades move from side to side. Too much and I'd have to think about pulling them all the way down and asking Litetek (https://litetek.co/Carb_Kit_Suzuki_GSF250-VY.html) if they have a kit. The bodies get a good clean in 3bond and the jets and other metal bits sit in a 3bond bath for a few hours. I noticed two of the diaphragms had been installed poorly. A little TLC should sort these out The manual says these carbs should have a #30 pilot jet. They have #27.5, so I might order some. The main jets are in good condition and the correct size (#97.5). The bowl rubbers were flatter than (insert whatever is really flat), so they were replaced by some nice new Litetek units. Hmmm...blue. The Litetek kit(s) I bought had a full range of new O-rings and seals, so there's no point not replacing them all while you have the carbs apart. I almost always find a washer or O-ring that doesn't really belong where it has been used, so replacing everything is my best policy. So, what else did I find... one of the carbs has a manufacturing defect. These Mikunis (damn you all to hell!) have a weird rectangular piece in the middle that holds the emulsion tube and also the carb piston/slider. It has an O-ring at the bottom and a rectangular rubber seal at the top. The ones in the following image are sitting upside-down. Anyhoot, one of them doesn't fit properly and it sticks out about 3-4mm into the venturi section. I think someone 'tuned' the carbs around the issue as best they could by changing the float height in the carb to compensate for the raised emulsion tube and subsequent needle position. After some time, I was able to 'modify' the carb so most of the piece sat properly. Unfortunately, doing any more would have caused damage, so it will stick out about 1mm into the oncoming air, but the fuel should be delivered closer to that in the other carbs. I have started reassembling the carbs, but the squished diaphragms will need a little longer to straighten out. By the way, the chokes on these carbs worked, but were very sticky, so I pulled them out (I do anyway) and replaced the rubber seals with new (Litetek) ones. What an absolute PIA these Mikuni chokes are. Seriously, who invents a plastic clip-on and puts holes into the carb body to install a choke? And don't get me started on those effing fuel floats and bowls . I'm going to have a cup of tea and a lay down.