a 1300 would most likely have a 30/31 pict carb was the point I was trying to get to and if single or twin port but that’s as much as my T1 knowledge goes .
My first question to my mate was "is it a twin port or single port?", it was a twin port. I didn't think to ask about the carb.
Good point on the porting! Still not conclusive, but definitely a point towards an up rating of some sort. Carbs are very easy to change so probably not a proper clue!
Yes, but the pressure would be low, and you arent fighting the compression, so movement would be faster so the leakage rate would be fairly low. Its looking for proportional values, not exact .. I wouldnt expect to see exactly 410.25 cc of water shifted on my engine, but if you tried a 1300 vs a 1641 you might expect to see a difference of maybe 20%.