Panther

It goes by vacuum and/or load not RPMS.... You've probably never run a big enough cam or had to idle one at 1000 rpms with little/no vacuum then.... Do a google search if you don't believe me....

In the meantime here's a paragraph;
"Stock engines can have high vacuum readings (10-18 inches at idle) and the Holley power valves with higher readings like 6.5 to 10.5 will work correctly. Long duration non-stock camshafts and other performance related parts can cause a problem, because engine manifold vacuum may be lowered with these performance parts and the power valve, if incorrect, will always be open, even at part throttle, leading to an overly rich air/fuel mixture. The solution is to choose the correct power valve and to do that you need a vacuum gauge.




I give up...carry on..

69-CHVL

Yes but the mains are activated by airflow through the venturis, not vacuum - vacuum is below the throttle blades. I agree the PV will open, but the mains should be inactive. If the mains got active, the motor would stall out fast. That Holley exerpt is not talking about idling, just overall operation which I agree with. My cam is a 231/239 .6/.6 110lsa and idles around 900 with 11" for the record.

Just have to agree to disagree

Panther

That cam is small, that's why you've never seen any problems.....

With a larger cam you have so much overlap and so little vacuum that you have to crack the throttle blades open and adjust the mixture screws further just to get the engine to idle and/or shift without stalling... If you go far enough you begin to expose the transfer slots and you begin pulling fuel thru the venturi's if you have the wrong power valve... It doesn't dump...it slowlly drips...and after 10-20 minutes you'll begin fouling plugs.

It's not rocket science it just happens when you have a big cam and you need to know how to set up the carb so that doesn't happen....whether it be proper power valve selection or by adjusting the throttle plate in the secondary...

racinfever

Raise the idle speed, just because it will idle that slow doesn,t mean it should. Big cam , big intake, big heads , try raising the idle speed, thus air speed for more vacuum & fuel adtomization.