hello,
my motor is a tecumseh vlv 60 of tecumseh and when i start him (two times pulling and he is starting), he runs not good .when i give more gas on the throttle than goes the valve open and close ,and the motor speeds up and down very fast.
when i let the cutter of my sit on mower runs than the motor runs better .
i have already replaced the spark plug and clean the carburator.
who can help me?

did you replace all the gaskets between the motor carb and air filter housing? Those carbs are VERY finicky if you don't get everything just right

there are also o-rings in the carb that if they are bad, the mower won't run coreectly

also, did you see how flat the metal part of the carb was? I have seen alot of those warp and need to be filed and or sanded down flat for them to seal completly