Motorcycle Repair: Sportster Issues, air fuel mixture, sportster 1200 custom

Question
Hello Sir,

I have a 2006 Sportster 1200 Custom (carb rubber-mount). It had 5000 miles when I bought it and the previous owner installed Vance and Hines straightshots.

Firstly, this is my first Harley, I've had various bikes from other makes before but the Harley is different.

My main issue is backfiring during decel, particularly when I get off the throttle and let the engine speed go down - first it decelerates and then I hear intermittent "fump" "fump" sounds, not loud, then I'd hear a pop or two until the popping frequency and volume increases. It's not totally unmanageable since it at least gives me time to downshift or do a little engine breaking but I'd prefer if I could eliminate the backfiring altogether. I've already tried adjusting the mixture screw 1/8-1/4 turn after every test ride. It even got to the point where the plugs would be black with soot (which means its rich, right?). I also tightened the exhaust bolts but there's still backfiring. I guess next thing to check would be intake leaks, but how do I do this?

I also have a more minor query with regards to starting procedure. Compared to my other bikes, this seems to prefer a lot of choke for a long time (over a minute) during starting, then I'd slowly put choke off to the point where it's barely stalling. I keep it there while I ride for a couple of blocks (slowly), then I push the knob all the way in. My question is, is it possible to start the bike with no choke but with the throttle slightly open? I've done this before and the bike I think starts better. Before I make this my main starting process, I'd like to confirm that it wouldn't harm the bike in any way.

That's it for me. Thanks in advance!

Regards,

Rob

Answer
Do your straightshots have baffels in them? Put the air/fuel mixture screw back where it was and go for a ride. pull the plugs and let me knwo what color they are. By the way, the air/fuel mixture screw only affects idle.
The sportster is a little cold hearted, so you will ahve to give it more choke. Chocking it until it warms up is fine and doesnt hurt anything.
Mike