As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SERVO WAS CLEANED AND RECERTIFIED, WHICH PARTIALLY IMPROVED ENGINE PERFORMANCE. ENGINE STILL BACKFIRED AT 1300-1500 RPM. CLEANED INJECTORS, WITH NO CHANGE. REMOVED AND INSPECTED FUEL DISTRIBUTION VALVE. FOUND SMALL AMOUNT OF LINT PARTIALLY BLOCKING PASSAGES AT NR3 CYLINDER PORT. CLEANED AND REASSEMBLED VALVE. RUNUP AND OPS CHECKS NORMAL.