Hi Alex; going back through my correspondance I suddenly realised who you were. Believe it or not, it was the better part of 15 months ago that I looked at your carb! The main thing to remember when changing jets on a carb is to keep a careful log of the change--both date and jet fitted. This way, you have a progressive record of your changes.
Have you tried re-fittingthe original (mechanical) pump and seeing if the outcome is the same? Abarth still used the mechanical fuel-pump even on the 695SS versions. If you do go back to the 'mechanical' you have to check that you have the correct amount of operating rod protruding through the spacer--it is 1.5mm when the rod is just about to START moving out--the amount protruding is adjusted by the number of gaskets either side of the spacer.
Is the 'weak running' experienced when the throttle is slowly opened or when it is 'snapped' open? Have you cjecked that the float is correctly adjusted (between 5 and 6mm between the float and the top-cover gasket when the carb top is held vertically, so that the float is hanging down).
Have you access to an exhaust 'gas analyser'? It would be wise to see what you mixture readings are before you start chopping and changing jets.
A good source of carb jets is:---"ROCKY Srl" (
www.carburatori-italia.it). They have a bigger range of jets than Eurocarb. I have used them and been very satisfied with the service received.
I have also found that sometimes, contrary to common-sense, you have to use slightly BIGGER jets on the less tuned engine---my current engine is 659cc (+0.4mm) and I have had to fit SMALLER jets than those I used with the 652cc engine---it is something to do with the 'suck' of the engine. The slightly bigger engine had more 'suck' so pulled more fuel through the jets, hence the need to fit slightly smaller jets. It might be that you have to go up a size, but as I mentioned before, it would be wise to know what the carb mixture is 1st.
