Hi Dave.
The tickover is a bit random, but it's the cough and stall on throttle application that is the bigger problem, although I suspect they are related.
You're not the first to say the inlet being rough should be ok, and others on a different forum also agree it may be a bit too coarse, but shouldn't be problematic.
I had a theory that on tickover, fuel could gather in the grooves in the inlet, (they are very coarse grooves) then as they overflowed an extra bit of fuel would get taken into the combustion chamber altering the tickover. Once they filled again they would overflow and do the same again, dozens of times per minute perhaps, hence a random tickover. On application of the throttle the extra air rushing through would empty the remaining fuel in these grooves and cause a temporary flooding, hence the cough and stall.
This theory had a less than luke warm reception on the Britbike forum, but I'm still quite keen on it🙂
Apparently there is a special type of filler used in modelling that could be used to fill the grooves, but I felt reluctant to trust the filler not to fall out at some point, so I forgot that idea. Not sure what tool could be used to return it to standard, except perhaps a long finger and some Emery cloth.
The inlet is 22mm, same as the carb, so that seems ok.
I have absolutely no idea regarding the state of tune of the head/valves/cam etc. Maybe I'll find out one day if I decide to strip it and take those grooves out.