MOONEY ACFT HAD ICING IN FUEL LINE CAUSING FUEL FLOW REDUCTION AND PWR LOSS. PLT LANDED; TALKED WITH FACTORY REPRESENTATIVE AND ADDED SOME ALCOHOL TO THE FUEL; PERFORMED SATISFACTORY RUN-UP PRIOR TO TKOF. AT CRUISE; 13000 FT; AGAIN THE PWR LOSS OCCURRED; PLT RECEIVED VECTORS FROM ATC AND DIVERTED TO ARPT FOR LNDG. RPTR ATTRIBUTES FUEL ICING PROB TO FLYING AT TOO COLD TEMP ALT.

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I HAD EXPERIENCED SOME FUEL FLOW REDUCTION AND LANDED AT PINEHURST; OR; AND THEN AGAIN AT KLAMATH FALLS; OR. AT KLAMATH FALLS I TALKED BY PHONE WITH AN ENGINEER AT THE MOONEY FACTORY. HE CALLED ME BACK AFTER TALKING WITH THEIR STAFF AND CHEMICAL ENGINEERING DEPT. THEIR RECOMMENDATION FOR ICING IN THE FUEL LINE; WHICH WAS EXPLAINED AS CRYSTALS COLLECTING IN THE FUEL SEPARATOR AND CAUSING BLOCKAGE; WAS MIXING UP TO 3% ISOPROPOL ALCOHOL. I HAD THE FBO ADD SOME IPA (99.7%) TO THE FUEL (ABOUT 1.5%). I DID A FULL PWR RUN-UP; AND THEN DEPARTED; CLBING UP TO 13000 FT WITH NO PROB -- NORMAL FUEL FLOW AND TEMPS OF THE ENG; AND NORMAL PWR. AFTER ABOUT AN HR; I BEGAN TO EXPERIENCE PWR LOSS AGAIN; AND A SUBSTANTIAL DECREASE IN FUEL FLOW. I ASKED ZOA FOR A VECTOR TO THE NEAREST ARPT; WHICH THEY DID -- TO CHESTER; O05. I WAS ABLE TO KEEP THE ENG RUNNING ON PARTIAL PWR BY USING THE BOOST PUMP AND THEN PERIODIC BURSTS OF THE HIGH BOOST PUMP. AFTER LNDG I WAS ABLE TO TAXI TO THE FBO ON THE FIELD. I CHKED THE FUEL AND COULD NOT FIND ANY WATER. WE STAYED THE NIGHT IN CHESTER; AND TOPPED OFF THE TANKS THE NEXT DAY WITH ABOUT 10 GALLONS OF FUEL. AGAIN I CHKED FOR WATER; NONE WAS FOUND IN FUEL. I DID A FULL PWR RUN-UP; AND THEN DEPARTED; CIRCLING THE ARPT; CLBING TO 8500 FT; REMAINING OVER THE ARPT FOR ABOUT 15 MINS. I EXPERIENCED NO PROBS; AND THEN PROCEEDED WESTWARD TO RED BLUFF AND THEN S TOWARDS SNA; PICKING UP MY IFR CLRNC. I REMAINED AT 11000 FT FOR THE REST OF THE TRIP. THE ENG RAN NORMAL. THE TEMP AT 11000 FT WAS 15-20 DEGS F. EARLIER; IT HAD BEEN BTWN 0 DEGS F AND 10 DEGS F WHEN I HAD EXPERIENCED THE PROB. APPARENTLY THE ENG DOES NOT DEVELOP ENOUGH HEAT TO KEEP THE FUEL LINES CLR OF ICE PARTICLES IN THE FUEL SEPARATOR ON TOP OF THE ENG; EVEN THOUGH THE COWL FLAPS ARE CLOSED. THERE WAS NEVER ANY VISIBLE WATER IN THE FUEL WHEN I CHKED; WHICH WAS DONE AT EVERY STOP; AND AFTER EACH REFUELING. UNTIL I CAN OBTAIN A BETTER FACTORY APPROVED DEICING SOLUTION FOR THE FUEL; I AM SETTING MY PERSONAL LIMITS TO NOT FLY AT ALTS OR SITS WHICH WILL BE BELOW 15 DEGS F. MOONEY HAS NOT APPROVED ADDITIONS OF PRIST; BECAUSE OF A POTENTIAL EFFECT ON THE WET WING TANK SEALANT. THIS SHOULD BE RESEARCHED THOROUGHLY AND QUICKLY. I WANT TO EXTEND MY THANKS AND APPRECIATION TO ATC; ESPECIALLY ZOA; AND OTHER FSS PERSONNEL FOR THEIR HELP IN LOCATING A REACHABLE ARPT; AND FOR THEIR RAPID AND COURTEOUS HELP. A GREAT JOB; WELL DONE! THIS EPISODE CONFIRMS THE WISDOM OF FILING IFR (OR AT LEAST GETTING FLT FOLLOWING) -- THE CTLRS ARE THERE WHEN YOU NEED THEM. IT ALSO SUGGESTS FLYING AT A SAFE ALT; TO ALLOW LNDG AT AN ARPT SHOULD PROBS ARISE.