40hp yamaha 2 cycle 403cc wont idle and very difficult to start

[investigatenow]

New plugs, good gas and new gas lines. Its very hard to start to the point im worried about tearing up the starter. It eventually starts then idles rough. It will run ok after that but still rough and shaky. When you shut it down its the same thing... hard to start again. Any ideas? Please

 

[99yam40]

test compression, spark, and timing
they are all needed along with the proper fuel/air mixture to get proper firing of the cylinders