The particular 28mm one I have is shit because it's impossible to set the correct idle mixture without the RPMs going crazy, the idle circuit seems to get blocked really easily, there aren't any idle jets available for it and every now and then the float bowl will get stuck so it leaks petrol all over the floor.

Well hopefully the professionals will get it sorted for you and not charge you an arm and a leg. I forgot about the coil, it could be arcing inside or something.