ENGINE POWER LOSS.

Narrative

I WAS TAKING OFF FROM SJC ARPT AFTER A NORMAL RUNUP. TKOF WAS ACCOMPLISHED FROM RWY 20L WITH A LEFT DOWNWIND DEP TO SNS. TWR REQUESTED I EXECUTE A LEFT TURN AS SOON AS POSSIBLE; WHICH WAS INITIATED AT APPROX 300' MSL. AS I TURNED DOWNWIND AT 600' AGL THE ENG SUDDENLY DROPPED FROM 2550 RPM TO 2150 RPM AND A STEADY MISS PREVAILED. I REQUESTED IMMEDIATE LNDG FROM TWR AND WAS INSTRUCTED TO FOLLOW A JET ON 3 MI FINAL. I EXPLAINED THE PROB AND REQUESTED TO TURN INSIDE THE JET AND LAND ON RWY 30R. TWR GRANTED THE REQUEST AND A NORMAL LNDG FOLLOWED. A RUNUP WAS MADE ONCE I WAS ON THE GND AND EVERYTHING APPEARED NORMAL. THE ACFT WAS LEFT AT SJC UNTIL A CAUSE FOR THE MALFUNCTION CAN BE DETERMINED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATES ACFT HAD BEEN SITTING FOR SOME TIME PRIOR TO FLT. EACH RUNUP WAS FINE. MAINT INVESTIGATION INDICATES PROBABLY A STICKING VALVE CAUSED PROB. JUST ONE CYLINDER AFFECTED. FLOWN SINCE AND PERFORMS WELL. RPTR FEELS TWR DID NOT ACCEPT SEVERITY OF PROB. HE HAD TO COME UP WITH SENSIBLE ACTION OF XING TO RWY 30R RATHER THAN FOLLOW A JET ON 3 MI FINAL.