C170 PLT ENCOUNTERS CARB ICING AND DIVERTS TO AN ALTERNATE FIELD.

Narrative

I WAS FLYING IFR FROM PLB TO PNE. CONDITIONS WERE IFR THE ENTIRE TIME. WE CLBED TO 8000 FT; PICKED UP LIGHT RIME AND CONTINUED UP TO 11000 FT. DURING THIS PERIOD WE HAD INTERMITTENT CARB ICING PROBS AND DECIDED TO DIVERT TO ALBANY BECAUSE OF THIS. AS WE DSNDED THROUGH 7000 FT; WE FOUND TEMPS ABOVE FREEZING AND MODERATE TO HVY RAIN. WHILE BEING VECTORED FOR AN ILS RWY 1 APCH; AT 4000 FT; WE BEGAN TO HAVE MORE SEVERE CARB ICING -- THE ENG FLUCTUATED FROM FULL PWR; TO NO PWR AT ALL. IT CONTINUED TO SURGE. APPLYING CARB HEAT ONLY SEEMED TO EXACERBATE THE PROB. AT THAT POINT; WE ADVISED THE TWR OF OUR URGENT NEED TO LAND. THE CTLR WAS MAGNIFICENT. WHEN WE REQUESTED SVFR; THE CTLR ISSUED IT AND ASSISTED US WITH VECTORS TO THE ARPT. THE CTLR ALSO DECLARED AN EMER ON OUR BEHALF. I CONTACTED OUR MECH WHILE ON THE GND AND WE SPOKE ABOUT THE PROB WE HAD. HE TOLD US THAT THE ONLY WAY TO RESOLVE THIS ISSUE WAS TO LEAN THE MIXTURE; AND THAT WE MIGHT NEED TO LEAN IT ALMOST COMPLETELY OUT WHILE AT THE SAME TIME APPLYING CARB HEAT. A CONTRIBUTING FACTOR WAS CERTAINLY THE CONDITIONS I WAS FLYING IN -- JUST ABOVE FREEZING TEMPS AND PLENTY OF MOISTURE. THE NEED TO LEAN THE MIXTURE UPON APPLYING CARB HEAT IN CERTAIN CONDITIONS WILL NEVER BE FORGOTTEN AFTER THIS EXPERIENCE.