I too have done the BB to my Deuce. The BB kit I ordered came with a new clutch diaphram spring. It came with the kit, so I installed it. It must be in there for a reason. I took the time to inspect the parts inside the primary case as well as check the chain adjustment since I was in there.
the big bore kit comes with a stronger clutch spring. i have seen a few post about clutches slipping without the extra pressure. if you bought a big bore kit and your dealer didn't put in the spring, i'd be asking why and where it is...lol