If you lean it out too much that will cause the power valve to try and compensate which will make it use more fuel if the vacuum signal is too low.

 

Ya I am on board with that. My vacuum is real good, 19" at idle and 15-16" at cruise. Even on steep grade never falls below 12". Only time my 6.5 power valve opens is on WOT or when I have my foot in it and that is almost never, I'm just a cruiser.

 

Tom, Jeff Smith mentioned that in the article I sent you yesterday. It might be necessary to install a somewhat higher rated PV, maybe a 7.5" or 8.5", to cover any lean spots or hesitation when calibrating a carburetor this way. Many people tune their carbs "backwards" in some ways, because so many techniques and components that work fine in full bore drag racing have bled over to general tuning advice even though they do not always translate very well to a street driven engine, especially someone focused on economical operation.

On the other hand some people ignore many of the tricks of the trade or knowledge that performance engine building and racing brings to the table, thinking "well that's for racing, doesn't apply to me." Course this is suppose to fun. Holley makes an EFI "carb" that works pretty well. To me it's the obsolete tech itself part of the hobby that interests me, that's part of it anyway. I don't even like LED headlights, they look weird to me.

And you kids get off my lawn!!

 

Tedster9 -- Well after I do my road test with a PV plug in the carb to make sure the PV was not messing with my system and checking the 8.5" power valve that is in my Holley 2300 to make sure it is working right maybe I will re-install it for know. My vacuum reading are fine for a 8.5 PV. Ted, I saw that in the Smith article.

So no one has answered yet !!!! Are the 15.5 - 16.0 cruise and 12.5 - 13.0 WOT settings the same for a V8 & 240/300 Inline 6?

 

I doubt it is based in any way on the number of cylinders, but more on the intake and combustion chamber design and things like that. Carbureted engines have trouble with somewhat lean mixtures because of intake runners, each cylinder gets a slightly different air/fuel charge. Some are leaner than others. So keep in mind at the same time, when you have an O2 sensor generally it's an average of one cylinder bank in the case of a V8, or even just a reading from single cylinder.

But the leanest cylinder out of the six (or eight) will determine the point where misfire actually begins. It's possible I suppose you might reach surging or misfire before reaching your "target" AFR. But 12.5 to 13.0 and 15.5 should be no problem for a Six cylinder as such. I've no doubt it's done all the time.

If you plug "power valve channel restrictors modification" and similar words into your favorite internet search motor it will have more on this. Lots of carb tuners out there that really take it to the next level, modifying idle air bleeds too. With the Holley and the metering plate it's popular to drill out the restrictors and install 6-32 brass inserts, and play with the size that way.

 

Thanks Ted,
Because the Holley 2300 2bbl has only one idle jet block and it is not considered a performance carb I am sure it will have fixed restrictor that can be drill out like we planed. We will see in a couple of weeks.