I bought a 550 that the PO had lost the spring clips, it ran like a bag-o-shite, I stripped the carbs and found all 4 main jets in the bottom of the float bowl. I used copper wire wrapped around the main jet holder/emulsion tube/needle jet (whatever you call it) under the hex head, then wrapped around the clip groove in the main jet. I did that 20 years ago, its still the same.