Hi dy2 ,sounds like it running weak mate,is there any water in the petrol?have you had the carb off and looked in the float bowl at all?what is the air filter like and is the vaccum tap working properly.also make sure the fuel tank capisnt causing a vaccum in the tank although after 30 secs it should be that really,but try it with the cap off anyway for the sake of it.also make sure the air filter is on the carb properly and the jets are clear in it.water will appear to look like jelly in the petrol and always be on the bottom of the tank and carb as its heavier than the fuel is.
adam bike doctor
May 2010