Small aircraft has engine quit. Switching fuel tanks enables restart but RPM variable.

Attributes
ACN	243759
Time
Date	199306
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : i39
State Reference	KY
Altitude	msl bound lower : 9000 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : lex
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 33 flight time total : 340 flight time type : 240
ASRS Report	243759
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

Small aircraft was refueled in OI8. After preflight contacted lex approach to open IFR flight plan. Cleared to 9000 ft direct loz. Uneventful climb to 9000 ft. After approximately 45-60 min flight, light RPM changes then engine quit. Established best glide and notified lex approach who vectored me to I39. Mixture, carburetor heat, and throttle changes did not correct problem. Switched fuel selector to left with no result. After switching to right, power came back but with RPM variations. Landed at I39 ok. Mechanic checked out fuel system and found the right fuel vent blocked. Fuel selector valve was ok.

Original NASA ASRS Text

Title: SMA HAS ENG QUIT. SWITCHING FUEL TANKS ENABLES RESTART BUT RPM VARIABLE.

Narrative: SMA WAS REFUELED IN OI8. AFTER PREFLT CONTACTED LEX APCH TO OPEN IFR FLT PLAN. CLRED TO 9000 FT DIRECT LOZ. UNEVENTFUL CLB TO 9000 FT. AFTER APPROX 45-60 MIN FLT, LIGHT RPM CHANGES THEN ENG QUIT. ESTABLISHED BEST GLIDE AND NOTIFIED LEX APCH WHO VECTORED ME TO I39. MIXTURE, CARB HEAT, AND THROTTLE CHANGES DID NOT CORRECT PROB. SWITCHED FUEL SELECTOR TO L WITH NO RESULT. AFTER SWITCHING TO R, PWR CAME BACK BUT WITH RPM VARIATIONS. LANDED AT I39 OK. MECH CHKED OUT FUEL SYS AND FOUND THE R FUEL VENT BLOCKED. FUEL SELECTOR VALVE WAS OK.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.