This data may be helpful to those of you who are tuning Webers, with or without a wideband AFR. it was collected from a series of full bore (WOT) runs in my 79 Spider. Most of the runs were in 3rd gear but a couple, identifed by 6500 rpm limit were in 4th gear. A complete description of the motor and its dyno curves are at http://www.alfabb.com/bb/forums/spid...ider-dyno.html
We jetted the Webers for maximum power and torque during dyno testing and we ended up with 150 main jets and 210 air correctors. For any motor with webers there will be a number of combinations of main jet and air corrector that will produce the same maximum power. The best combination will usually be the one that gives the broadest power and torque bands. It is clear from my dyno sheet that my torque dropped off at lower rpm as the AFR went low so my objective was to investigate other jet combinations that produced the same AFR at maximum power rpm but gave a higher AFR below 5000 rpm. During this testing I learned, or was reminded of three things:
1 - idle jets have no effect on the power curve with emissions Webers
2 - Changing the air correctors will lift or lower the complete curve with less effect at lower rpm.
3 - Changing the main jets will raise or lower the low and mid range and have little effect at high rpm unless the jet is too small for the motor. In other words if it has fallen outside of the range of allowable combinations. When that happens the whole curve goes lean in a big way.
I have posted a couple of screen shots of data plots in Excel.
The first shot shows the effect of 145, 140 and 135 main jets with 160 air correctors. You can see that the upper range is about the same with 140 and 145 and that 140's give higher AFR's in the lower range. You can also see the effect of a main jet that is too small.
the second shows the the effect of changing from 210 to 230 air correctors with 150 main jets.
So for my motor 140 main jet with 160 air corrector gives a similar AFR at peak power to the 150 main jet/210 air corrector that we arrived at on the dyno. The 140/160 is preferable because while staying in the safe, sub 13.5 range at all times, it is within the optimum power AFR of 12.5 to 13 for a broader rev range and it lifts the AFR in the low range where it is clearly too rich. This is shown on screen shot #3.
I tried to attach the Excel file with all the raw data and graphs but it is too big. Pm me with your email address if you want a copy.
My next step will be to try some richer idle jets to try to eliminate a little hesitation from closed throttle. Then some exhaust work is planned.