My 'Doba is backfiring when i stab the throttle. In park or under load. I found that all three hoses from the vacuum canister were dry rotted and split. Replaced them. Changed plugs gapped to .035. New air filter. Upon starting cold did not backfire. Fter about a minute of running it started doing it again. I did notice that the old rear passenger side spark plug was full of deposits and almost burned off like at the tip. Have not changed egr valve or pcv yet. also have fuel filter to put on. Carb rebuild in order? BURNT VALVE? I hope not...