I would suggest this:
Grab goliaths old carby, pull it fully apart, and gather the following parts from it:
-The Body
-The Main Jet & Tube
-The Throttle Slider (The larger grey thing from inside)
-The 2 springs
Now, carfully clean these, paying close attention to the Jet and tube
Take of goliaths new carby, fully, and pull it apart.
Now, take the G4 body, and fit it to the air hose securely, with the throttle cable locked into its notch.
Slide the control on the handle bars up and down, and make sure it is going in and out inside the body of the carby.
Now, take the throttle slider from the G4 pile, and fit it into the body, making sure the ball at the end of the throttle cable locks into the hole in the throttle slider.
after this, place the lifter (the circle with 3 arms) over the top of the throttle slider, making sure the arms are in the 3 matching slots on the inside wall of the carby body.
Now turn it over, holding everything in place with your hands, so that you are looking into the hole that goes on the engine.
Take the poppet valve (looks like a car port valve, but plastic) and put it through the little hole in the middle of the carby body, so that the pointy end would be pointing away from the engine mount.
After this, turn it back over, and make sure the poppet vlave stays in place.
Put the small spring (from G4) ontop of the lifter, then the diaphram, fit it flat side up, and push the poppet valve point through the diaphram centre.
Then fir the locking clip form the G4 (It may be a little clip, that fits under the edge of the poppet arrow head, to lock the diaphram in, or it may be a bigger plate.
Now put the large spring over (the one from the G4) and clip on the good end cap.
Now fit the float components at the side, making sure to use the original G4 jet screw and tube.
The instructions for the cut out are
Here.
