Cut out at speed

[The sweetman]

When im flat out i can get to 27mph the motor had been running in the 30s fine but now it dies at 27 and engine picks back up when it slows

Its a 66cc with a gutted exhaust window piston and mild porting 42 tooth rear

 

[crassius]

sounds like the surging one sometimes gets when carb is shaking too much - offset intake can cause that, but it is usually loose motor mount or cracked frame