Well, The first thing you have to understand about these carbs is they only have really 2 running modes
1: Low speed (no load) throttle plate closed
2: High speed (any throttle setting other than Idle)
A: The carb draws all of it's fuel threw the main jet on the bottom of the carb bowl.. (this can be eather a needle that adjusts or a bolt with a meter hole)
B: When the carb/engine is at Idle (throttle plate closed ) all of the air it draws in is speeding by the edge of the closed throttle plate by the LOW speed orifice's (these line up roughly with the low speed needle mixure screw side on the carb)
C: When the engine is not getting enough fuel at the Idle setting, The govenor senses RPM loss and opens the throttle (thinking load is bogging down the motor), The motor starts to draw fuel through the main jet orifice ( behind the choke plate, a brass tube that sticks up and sprays fuel into the airstream), When the Main jet take control of the fuel load the RPM's Rev for a moment, The govenor senses the motor overspeeding and corrects it by closing the throttle plate bringing back to idle, But the low speed circut is running too lean and cannot maintain idle... So again the motors govenor trys to open the throttle to bring up/ maintain the idle RPM... And this happens evertime the motor goes REV..... REV.......REV.
Don't mess with the govenor yet... it most likely is ok...
Now first thing you should do is turn the low speed jet out (counter-clockwise ) about 1/8 turn (while motor is trying to idle)... see if the osolations (rev..rev...rev) changes or goes away.. If it doesn't, turn it till the engine starts to run rich and blubbers - then slowly turn it clockwise till it cleans up/ sounds better...
You can adjust the High speed fuel jet (under the carb bowl) about the same way.... Put the throttle in the high speed position and have the engine at full speed.... If the motor is blubbering/ running rich turn the screw (high speed fuel jet under bowl) clock wise to lean it up, or counter clockwise to richen it up....
Now here is a note about the high speed adjustment, A motor running at full speed with no-load requires less fuel than a motor running at high speed under load. (meaning the jet needs to be turned richer slightly from where the engine runs best under no load)..
Try that...If it does not improve, let me know what symptoms it has from there...
Good Luck,
Friiy