wigan,
If the carby is made in Mexico you need to do two things replace the filter in the tank and also the filter in the carby itself (or just remove it).
The problem is that because the filter in the carby is such a tight weave mesh it blocks really quickly and reduces the fuel flow which causes the problem.
This is providing that the cylinder is not damaged but you did not mention that it was when you removed the exhaust.
Hope that this is of some help.