Johno, please let us know whether replacing the diaphragm makes it work better. I'm assuming you have replaced the spark plug - doing that brightened mine up somewhat. The engine runs quite well at full scream, but does poorly otherwise. I think a smaller carburetor might make it into a decent machine - at 16 cc it really is a tiny engine, and seems to give maximum speed and power with the throttle set to the start position, which is less than a quarter open.
