A thumper carb jetting question

[Black Knight]

I recently purchased a Jap language Factory Service Manual for the Honda GB400 and it shows pilot jet at 45 and main at 168-My GB500 FSM states pilot at 48,which is fine,but the main at 152.-Is it correct that a bike with 100cc less would have a main jet 16 sizes higher?It doesn't quite seem right to me.Any carb gurus out there can answer this?-Cheers.

[Grumph]

Probably, yes. If it's the same carb, airspeed on the 400 is lower hence less vacuum on the jet - so the jet has to be bigger to get the correct mixture.
152 vs 168 isn't a huge difference either.

[Black Knight]

Thanks Grump-This same thought occurred to me late last night,20% less vacuum will require larger jets,it was the 152 vs the 168 that surprised me,I also realise now that it is only six sizes so I can rest easy.Thanks again.