Presentation of the strengths and weaknesses of the carburetor 24/26 and 28 (size venturi)
 
The Mikuni VM26 and VM24 were floats too heavy does not always perfect closure of the faucet system. This causes overflow fuel enrichment. You must adjust the float position at the lowest as possible.
Their valve sometimes don't close when outside temp is under 10°C ! Great effect. There are VM26 preset for 4 stroke and 2 strokes. The difference is much greater than simply adjust the jets. A 2-stroke carburetor of a 4 stroke does not work well at all because the suction is very different between these two types of engine.
The Molkt 24 (that some importers announce in 26 falsely), works well on any type of engine. Not the best at low rpm. Better in fast turn with a longer slow jet.
 
Keihin PE26: more power than the Molkt 24.
 
Keihin PE28: for racer rider. Ours have a non adjustable needle that works very well everytime.
The PE28 from Daytona have an adjustable needle but not working right sometime for pitbike use !