PLT MAKES PRECAUTIONARY LNDG BECAUSE OF A ROUGH RUNNING ENG.

Narrative

PRIOR TO FLT; THE ACFT SPARK PLUGS WERE PULLED; CLEANED; GAPPED; AND REINSTALLED BY THE OWNER/OPERATOR AS ALLOWED UNDER FAR PART 43; APPENDIX A; (C)(20). ALSO COMPLIED WITH MFG SVC BULLETIN ON CARB HEAT VALVE GASKET INSPECTION. ACFT ENG RUNUP CHKED OK. ACFT TAKEN ON MAINT CHK FLT. ACFT PERFORMED ADEQUATELY. FLT ALTERED TO SURVEY LCL FLOOD CONDITIONS. CONTACT MADE WITH LCL TWR FOR FLT ALONG FRINGE OF ATA. CONTACT MAINTAINED AND TFC CALLED AND ACKNOWLEDGED. 35 MINS INTO FLT; ACFT ENG ROUGHNESS OCCURRED. PLT ELECTED TO MAKE PRECAUTIONARY LNDG ON ABANDONED ROAD NEAR RIVER. ALL NECESSARY TOOLS; INCLUDING A TORQUE WRENCH; WERE ON BOARD THE ACFT. LEANING MIXTURE AND HIGH PWR RUNUP BURNED OFF PLUGS. PLT PREPARED FOR TKOF AND WAS STOPPED BY HWY PATROL. CALIFORNIA HWY PATROL OFFICER CALLED AWAY AND TURNED SIT OVER TO COUNTY SHERIFF OFFICERS. AFTER MUCH DISCUSSION; PLT WAS ALLOWED TO TKOF WITH ADMONISHMENT. AN AUTOGAS STC IS CURRENTLY NOT AVAILABLE FOR THIS ENG/AIR FRAME COMBINATION. USE OF 100 'LOW LEAD' WILL CONTINUE TO CAUSE FOULED PLUGS AND ROUGH ENGS. TCP AVGAS ADDITIVE IS USED ROUTINELY IN THIS ACFT WITH NO NOTICEABLE RESULTS.