Small Engines (Lawn Mowers, etc.): 2stroke victa, head gasket, main bearing

Question
the engine revs flat out.The throttle cable works but will only shut the engine off.I have replaced the gaskets and replaced the carby 3 times off other mowers that all work well.Sometimes the engine will drop revs and then rev back up seconds later.Do you have any suggestions

Answer
HI DAVID

1) HAVE YOU CHECKED THAT VACCUUM LINE  FROM C/CASE BUTTON TO CARB DIAPHRAM IS IN PLACE AND NO HOLES

2)HAVE YOU CHECKED THAT THE VACCUUM BUTTON ( BETWEEN FLYWHEEL & C/CASE HOUSING ) IS CLEAR OF DEBRIS ?

3)HAVE YOU CHECKED THAT DIAPHRAM IS CORRECTLY SEATED AND SEALED OFF WITH WITH THE CAP ON THE CARB AND THE LONG SPRING IS RESTING ON STEEL PLATE ON DIAPHRAM AND ALSO IS LOCATED INTO RECESS IN CARB CAP      IF ITS NOT SEALING OFF ENGINE WILL REV EXCESSIVLY

4) MAKE SURE THAT THE O RING UNDER THE STARTER ASSY IS OK AND NOT LEAKING
THIS WILL LET AIR INTO CRANKCASE  AND REVS WILL RISE

5)CHECK THE MANIFOLD TO ENGINE BLOCK O RING AS WELL

6) HAVE YOU CHECKED THAT DECOMPRESSOR IS FUNTIONING CORRECTLY  AND IS NOT LETTING AIR IN WHEN IT SHOULD BE CLOSED , CHECK PIPE THAT ALLOWS VACCUUM TO DECOMPRESSOR  

YOU MENTION THAT HAVE TRIED CARBS OFF OTHER VICTA  ENGINES THAT WORK FINE  BUT YOUR ENGINE STILL DOES SAME THING - CORRECT      THIS THEN TELLS  ME  IT SOMETHING ON YOUR ENGINE  

PLEASE CHECK ITEMS  1  - 6   ABOVE THEN IF ITEMS ARE OK  THEN I WOULD SUSPECT A AIR LEAK FROM EITHER  C/CASE MAIN BEARING SEALS , STARTER O RING ,   POSSIBLE CYL HEAD GASKET   BASICALLY A BIG AIR LEAK    NEED TO FIND IT   2 STROKES NEED AIR TIGHT C/CASES TO OPERATE PROPERLY  

PROVIDED  MUFFLER IS CLEAR AND COMPRESSION AND SPARK ARE OK AND UNIT IS GETTING CORRECT AMOUNT OF FUEL  AND CARB IS SET RIGHT SHOULD RUN

PS  VICTA NEED  ABOVE 60 -70 PSI COMPRESSION TO RUN GOOD , MAKE SURE MUFFLER IS CLEAR

HAVE  A GOOD LOOK  AND LET ME KNOW WHAT YOU FIND  


CHEERS HOPE IT HELPS  

PAUL