I have a 92 sportster 1200, while riding to work the other day it started missing and coughing when gas applied, it idles fine, I got it home cleaned carb, checked intake seals, still no go, switched to a older carb that ran fine, no go, tried new ignition and replaced the ignition plate sensor and coil. still starts fine but as soon as gas is applied it coughs out the carb, backfires out the exhaust. the headlight dimms as it coughs. any ideas.... ? [&:]