I have a well built 17.5 and I have noticed that it has a small miss between 5-6k rpm. Any ideas on what this could be?
Is it a gradual loss of power, or sudden loss of power?
Does it clear up past 6,000 RPM?
What do your spark plugs look like? Drive it into where it messes up on you, kill the motor. Read your plugs.
Thoughts:
Carb out of adjustment
Weak Valve Springs
Lean Engine (What's your head v.s exhaust temps?)
Fuel pump plugged with debris
Sticking carburetor needle
Plugged fuel bowl vent
Ignition coil breaking down (What's the coil gap?)
Mechanical drag (Iffy)