That’s great advice Mikeonabike.
|My initial thoughts are that your main jet is playing up. There could be several reasons for that as explained by Mikeonabike.
When you have access to the carbs before you strip them down lift the sliders together and make sure they drop smoothly and together. If one is faster than the other this could indicate a diaphragm problem.
If the carbs turn out to be fine then it could be the strength of the spark.
One of our members (Trevorbuster) had a similar issue. He had a low voltage reading at the coil so a weak spark was present. he fitted a relay to give a coil feed direct from the battery which he claims has massively improved his running. He is not an internet kinda guy (as is the case with several members) but has sent me ths details which I will post up in the near future,