If you haven't found the problem yet, looks like you still have the OEM pipes. I'd start there. Old cats, less flow, etc.

Malky1400

Any feedback if the problem is sorted? If yes what did you do?
I had/have a similar problem. Romans gave me a map that removed almost all of it except for a noticeable stutter at 3000rpm. (Before it was between 2500 and 4000 rpm.) Still working on it though. It doesn't effect the power of my bike it's just annoying when riding and you get this stutter.

Hey guys...thanks for all your feedback on this. I've not been on here for a while, but I did make a change to something on the bike, but not 100% sure if it's worked or not! only managed about 10 mile since fitting it, and it was a wet miserable day, so never had a great chance to give it a good blast, but after listening to various ideas, I opted for the O2 eliminator..the lambda probe bypass plug...only cost me £11, so didn't burst the bank, but I'll not know for sure until I get a better run. Thanks for all your help, I'll update this again when I'm next out.