89mustang with 306 E7 rebuilted heads. split cam 471. lift flat tappet, coustom built 650 QuickFuel carb. had a bad lifter and replaced run no miles with bad lifter hear it in shop on start up. But now i have a backfire though carb when i try to accerate for idle sitting in driveway and wrost on the road. If advance timing go way a little but still there but car backfires on start up then. DO I NEED TO JERK OUT ENGINE AND PUT A NEW ONE IN.