43F stuttering in high RPM

[stubbs]

my 1986 43F is running fine in the low rpm. but in high rpm it starts stuttering.
I already cleaned the carburettor, so this should not be the problem
And I am not entirely sure if its the motor thats stuttering because the motor runs fine even in high rpm when the transmission is in Neutral.

any ideas?

[ActionManMelb]

What RPM are we talking about?
I have found them to be unhappy over 7000rpm due to valve bounce.

Beside that, your number one suspect is adequate fuel supply.