what course of action is indicated?

bikerfox wrote: Thanks for your replies. There's no vacuum info given (although it was 11" @ idle) and no BSFC that  I can see, although when the car was being dynoed I vaguely recall that acronym on the screen.  Yes, there's room for secondary blocks and I've thought about  going that route.  There is no surging going on and a stumble was fixed.

I believe that to cure the stumble, the tech enlarged the pump discharge nozzles.

BassBoat wrote: just my 2 cents.  You adjust full power AFR by changing the PVCR for the primary and the secondary orifices in the plate which is harder to do.  Stock 600 -9 are too lean for single carbs.  What are you running now?  Adjust the primary jet for driveability.  I think messing with bleeds is a smaller fine tuning thing.  Full disclosure I tend to leave them alone.   You might find that quarter mile performance is better with a richer, maybe 11.8 AFR than typical 12.5 WOT target for max power.  but 10.0 is too rich

bikerfox wrote: 6PakBee wrote: It's a pity you don't have the BSFC numbers.  That, IMHO, is one of the first things you want to look at as it is an indication of how efficient the engine is.  If it is relatively constant that is a good thing.  If it is all over the place, falling, or rising with rpm, then you have some kind of problem.  A/F ratio is not the entire answer. From what I've gathered, BSFC is measured on an engine dyno.  I'm doing a chassis dyno.

The PVCR is the hole that the power valve opens.  The 5.5 number you reference is the vacuum at which it opens.  How much fuel you get when the power valve opens determines the total fuel.  On the primary, there are two sources of main fuel, the jet and the PVCR.  If you have too big a jet, you get too much fuel when you are just driving around.  If you get the driveability right, then that will tell you the primary jet is right, then you open or in your case close the diameter of the power valve channel restriction to get the AFR where you want it.  I would suggest trying to run with the secondaries disabled, and getting the AFR right on the primaries.  Then see what happens with the secondaries.  I missed that you had 450 CFM carburetors, sorry, so my reference to the -9 secondary plate applied to a 600 cfm 4160.  I like to get the plates that allow you to change jetting with conventional jets.