Unable to get rid of lean spot

[ArmandTanzarian]

I fitted my stage four iron barrel with a TM24 and an Ancillotti pipe. I did lots of trouble free miles until the exhaust (which appears to be made out of some sort of cheese rather than steel) fell to bits. I bought a JL3-road Curly pipe which ran well but although I tried all sorts of jet/needle combos I couldn't get it sorted. I would take it to the point where it started to "machine gun" and then go down a jet or move the needle a notch. It ran well but would overheat like a b@st@rd and checking the plug showed it to be slightly lean.

I've finally got hacked off with the whole thing, welded the Ancilloti back together (again) and refitted it.

Any tips about the JL and why it was such a sod to set up? I might have another go with it over winter. Is it a case of having to use a Dyno? The line between too rich and too weak seems like a bl00dy razorblade.

[Train Driver]

classic rapido 225 no tuning just cleaned up the rough edges, 24mm mikuni and ancillotti exhaust, this is my jetting which after 2500 miles is still spot on.
Jb dyno'd
main jet 175
pilot 20
needle 5n1b
hope this of some help