Frustrating acceleration problem!!!

I don't know what suitable jet upgrades would be for the 1300 I'm afraid. You can try going up a size on all the idle and main jets; try one upsized jet at a time and see how it drives. It might be worth asking what 1300 owners have done on Xweb, there are more 1300s over there!

I'm so pleased as I have now managed to sort out the running of the car!!!!
As I have another carb in my garage, I decided to take off the existing primary main jet (1.10mm) and swap it with the secondary main jet (1.15mm) from the other carb. So now both primary & secondary venturis are running with 1.15mm main jets. The hesitation has now disappeared. Must be the CSC exhaust system that has caused the car to run lean.
Just wanted to say thanks to all you guys for your help/ advice, least my carb has now had a thorough clean.

Great news - glad it was a simple fix in the end!