Mine did this, I reassembled and tightened the clamp, then carefully balanced the throttle bodies with a Morgan Carbtune...one Saturday run later it had gone again, so I lockwired it. 12,000 miles later - no issues. The bike only backfired/burped after the boot was off, not before and not since its been lockwired on.
Access is easy, after losening the fairing panels at the side of the tank & removing the rear bolt you can lift the tank and have a look at the rear inlet - youu'll know if its off as you'll see the lip of the inlet it sits on...you can push it back down and tighten the clamp, if you are lucky, that'll be it. If not, then lockwire it on using the lugs as shown in Greywolf's photo.
After realising how damned fiddly access was to the vacuum take-offs I ran a couple of vacuum hoses from the stubs on the cylinders out to the underseat area and now I balance my throttle bodies easily. The blue 4mm silicon hose I used was pennies off e-bay.