EMER DECLARED FOR PRIORITY HANDLING IN FORCED LNDG AFTER GAR ATTEMPT.

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BECAUSE ANOTHER ACFT WAS ON RWY DURING MY FINAL; TWR COMMANDED ME TO GAR. I COMPLIED AND ADDED FULL PWR. ENG COUGHED AND HESITATED. I ELECTED TO IMMEDIATELY REDUCE PWR AND CIRCLED R INTO DOWNWIND; BASE; AND SHORT FINAL FOLLOWING A RADIO CALL TO TWR; INFORMING THEM THAT I 'HAD A PROB AND REQUIRED IMMEDIATE LNDG.' A NORMAL LNDG WAS MADE ON RWY 24. I RECEIVED LNDG CLRNC AND WAS INFORMED THAT FIRE EQUIP WAS ROLLING. THE FOLLOWING MONDAY MECHS FOUND THE ACCELERATOR PUMP DISCHARGE TUBE FROM THE CARB MISSING. CONSISTENT WITH PIECES OF DEBRIS FOUND EARLIER IN #2 CYLINDER (UP 'TILL NOW UNEXPLAINED) MY AIRBASE STATES THIS IS A FAIRLY COMMON PROB WITH CARBS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS IN A PA-28-140. THE FAILED PART; THE ACCELERATOR TUBE; WAS CITED BY THE MAINT FACILITY AS HAVING BEEN INVOLVED IN 'SEVERAL' INCIDENTS REFING ENG PROBS. THE ACCELERATOR TUBE AFFECTS THE ACFT'S PERFORMANCE CAPABILITIES IN ANY RAPID ACCELERATION DEMANDS UPON THE ENG. THE RPTR HAS NOT HAD TO RESORT TO ANY 'SPECIAL' PROCS REGARDING THIS CARB PROB. HE STATED THAT; SINCE HE ALWAYS CUTS OPEN HIS OIL FILTER AFTER CHANGING OIL AND FILTER; THIS PROC WILL COVER THE CARB ACCELERATOR TUBE SIT (SO FAR AS A PROGNOSIS OF PARTS COMING UNGLUED). THIS IS THE WAY HE CAN CHK FOR ANY METALLIC PARTICLES WITHIN THE FILTER AS A GAUGE OF ANY INTERNAL ENG DETERIORATION. RPTR IS VERY CONSERVATIVE REGARDING HIS MAINT PROCS. HE CHANGES HIS OIL EVERY 30 HRS VERSUS THE 50 HRS ALLOWED OR RECOMMENDED.