Join Date: Feb 2003
Location: New Jersey USA
A 45 has a smaller fuel orifice than a 50 but that does not necessarily make it leaner (the two digit number is the diameter of the orifice; a 45 is 0.45mm, 50 is 0.50mm, etc). The other part of the equation is the 'f' number. This designates the number of and the diameter of the air bleeds. Thing is, the f numbers are not in any particular order according to size so one needs to look at a chart of Weber idle jets.
Series 2 USA 1750 GTV (in Series 1 European clothing)