Hi Chasaduc, The factory has run a couple of different jetting setups in the webers on the 750.
Before the middle of 1987 the jetting was 142 mains,160 air correctors and 60 idles.This would have been very rich down low with th 60 idles and stumbled around the 2500 - 3000 rpm mark.Today I ran 145,160,55 as an experiment and there was a tendency to go a bit lean around the middle of the rev range.The 60 idles would have fixed this problem,so this jetting was probably fine through the rest of the rev range aside from the rich stumble.
After the middle of 1987 the jetting was 150 mains,170 air correctors and 57 idles.They reduced the size of the idles,IMHO to alleviate the rich stumble,but this would have leaned the middle of the rev range, so they increased the main jets by almost two full sizes,while increasing the air correctors by less than one size,this would have richened the whole upper power band up especially wide open throttle.
I am currently running 150 mains,160 air correctors and 55 idles,this is richer than factory across the middle and top end of the rev range,but will hopefully allow me to drop down to a 54 or 53 idle as I still have a rich stumble condition at 2500 - 3000 (if I open the throttle quickly the accelerator pump shot causes the problem).A 50 idle creates a lean condition at 5000-5500 rpm,which is difficult to get rid of so is too small.
The current jetting is perfect for my bike when cold,but when hot is just a tiny bit rich.If I can't get rid of the rich stumble by reducing the idles,I will stick with this jetting and play with float levels,accelerator pump jets and emulsion tubes to fine tune it. I think this would be a good starting point for you if you are not happy with how your weber is running,but it is hard to say without knowing your climate and altitude.Idle jets are only about $3.00 each on ebay so buying a half dozen to play with won't break the bank and they are very easy to change without dismantling the carby.The jets are available in single increments and it is amazing the difference 4 or 5 sizes of idle jet can make to the running of your bike,when you start to get close to a correct size.
In my experience using a lamda meter as a guide,a stumble down low (2500 - 3000) is a rich problem,remedied by reducing idle jet size and a stumble up higher (4500-5500) is a lean condition,that can be fixed by increasing idle jet size,the trick I think is finding the balance point,which makes the bike most rideable and then fine tuning the other variables(main jet,air correctors float levels etc.)
Hope this wasn't too confusing  and is of some help to you. Jay.
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