99 suzuki katana 600 exhaust issue startup problem.. help..??

Hey Folks!
I've recently acquired a '99 Suzuki Katana 600, which I'm totally loving being on.. however, there's couple of things which do makes me a bit uncomfortable, and I can't help thinking of fixing them somehow..
just fyi.. I've recently got the Jets changed (replaced a new kit) with the fuel flowing richer than usual..
Now, for starters, I'm facing ignition / startup problems in the morning.. although it's cold here, but still it takes quite a while, and after starting the first time, the rpm gets lower and lower and ultimately the engine stops.. (even using choke)
Then comes the part where I have to throttle it a bit to start, and it gives out quite some smoke too..
Soon after it's up, I still get the engine cutting off on me at certain points, as if the exhaust is choked.. there's quite a lot of backfire pops from the exhaust.. and that continues for the whole time I ride it afterwards..

So, I hope you've got the scenario, and can guide me in the right direction.. :)

Thanks in advance..

J.