Hello everyone. I just picked up a 1990 VN750 and am having problems with a backfire. After starting the bike with the choke, there is a noticeable backfire every 4 to 5 seconds followed by a pronounced 200 - 300 bump in RPMs and the cycle repeats. The backfire seems to be coming out of the exhaust pipe attached to the aft cylinder. Also, on deceleration there always seems to be two to three smaller backfires. Any thoughts on the culprit?