don't mess about changing the dashpot spring or anything in the carb,,,use standard engine oil in the top damper......try and set it up without doing anything to the needle,,,1st get it to idle,,,ie set the throttle stop so the engine is running around 1000rpm and then wined the mix screw in or out only 1/4 turn at a time and find a point were the engine rpm is at its highest....then bring the idle down to around 800rpm by the throttle stop adjuster......
Then try it............let me no what its doing after a road test