You're welcome. Glad I could help on that one. Let's face it. This is a tough subject to explain clearly, and then sometimes even the most knowledgable ones either misunderstand or mistate, or just jump in their thinking in way its hard to follow.
Quote: Am I correct in understanding that with a flat fuel curve of say 12.5 at WOT the mixture will still go lean on medium acceleration before the PV opens?
Correct. That is the way fuel delivery is normally set up. Perhaps the best graphic of that is the one from Obert in Tuners post.
Quote: And that if you get problems you can't fix them with a different air bleed?
If you're asking about part throttle problems, I wouldn't say can't, but it didn't fit the description of the problem you described. As you saw in both those charts that you referenced, the main air bleed has the most impact on the mixture when the circuit starts to operate and as it gets toward maximum flow. My experience and observations has been that the main circuit is providing most of the fuel when holding a steady speed around 60 mph (3000 rpm). In otherwords, around this point it has just fully taken over from the idle circuit. Changing the main air bleed (MAB) will likely start the mains a little sooner or a little later. But it will also effect the mix at the top of the rpm range.
So if you've got a nice flat AFR at WOT, and you change the MAB, it will effect the AFR at the top of the WOT. In my thread A little Dyno Fun: Disconnecting Secondaries you can see that the Primary MAB is pretty close but the Secondary MAB (and or e-holes) are not a good match.
The situation you described was that getting maybe 70% into the throttle, the load was too much for the lean AFRs. Looking back at Tuner's post #17 linked above, see the pages from Larew and Taylor have need to go richer at different loads. The one engine needs richer mixture at near 90% maximum load where the other somewhere around 70%. So your PV is opening by 90% load, but maybe not at 70% load. A higher power valve woild take car of that.
I'll also attach an AFR table (using E10 pump gas) from my own setup last September. It's not perfect by any means but gives you an idea of the relationship with vacuum and rpm. It includes only data from when the throttle was steady. The larger vacuum numbers for any given rpm are when the engine is light coasting and very light (nearly closed) throttle. [right click to see it full size}
Somewheres in the Innovate forums you can find some discussions of PV tuning. Some practical, some informative but unless you have access to a 4 or 5 gas analyzer, just informative. I've spent hours there digging back to the begining. Slowly I've absorbed some of it.
