T140 Main Jet Issue

I know this is an age old question, but I have a '76 T140 with baffled TT pipes and tn32 mikuni carbs with velocity stacks. My problem is when accelerating the bike splutters. My thinking is smaller main jets which I have tried (although maybe not far enough), I've also tried bigger jets but that didn't work either. Am I right in thinking I need to go smaller as this is getting expensive (at x2 mikuni jets!). Thanks for any help.

 

Not sure as I haven't got a rev counter, but it's 3/4 throttle and up. It was running ok on Ramair foam filters, so pretty sure it's main jet as it's only started since I put on the velocity stacks on. I know the answer people are going to say from that, put the foam filters back, but it doesn't answer the question.

 

Yeah I've only moved the needle clip up one notch, but I'll try moving it again at the weekend. Thanks