Problem just started last night. Started it up just fine but as soon as I took off it started sputtering and backfiring with black smoke being released from the exhaust. Looking for any advice I can get as to what might be the problem and how I might be able to fix it. My bike is a '94 kawasaki vulcan 88. Recent work includes new spark plug caps and a new master cylinder. Sorry if there was a better place to post this, still new here. Thanks in advance.