if your air fuel screws dont seem to do a thing then your primary idle screw is turned up way too far,,to get rid of a off idle stumble you need to use the secondary screw to raise and lower your idle..you want like a 1/4 turn o n the primary idle screw and no more that 1/2 a turn on a/f screws..the further out you turn them the more your eyes burn..and all the engine will do is load up the further out they are..

if the idle air circuit is not properly adjusted you will have a major stumble and it wont matter what pv or what jets you have or squirter or throttle cam you change its still going to do it..

Good info Mike. ICDEDPPL dan had a lean sneeze issue with his carbs. I went through both carbs, and reset all throttle blades and mixture screws to spec. Did some fine tuning on the water after. Long story short, it doesn't sneeze anymore getting on plane.

Idle mixture screw definitely make changes to the idle and AFR's. What i'm saying is that i can't turn them out any further than a 1/2 turn without the engine going "pig" rich. Actually, it idles very well. Very clean and smooth for the size cam it has. Those numbers were at .050.

Update-I installed the 4 window #6 PV and no change noted. Decided to change the primary squirter from 31 to 33. Same crap. Measured PV ports to be .065. Kevin from CSU .054 should be stock. He won't sell his PV alone. Steve Morris engines quoted $3300 for the fuel inject setup needed with initial programming. So....looks like I have a PV to make tomorrow. Time to get a friday buzz on.

you do have jet extensions ??? when the carb is under pressure it will push the fuel to the back of the carb and wont allow any fuel to the jets..they need to be extended to the middle of the float bowl to prevent this from happening..

also,timing?

what sparkplug?

what spark plug gap?? this is important..

are you using a boost referenced fuel pressure regulator??

Ok, back to original post question....where does your power valves pick up vacuum ?? different carb guys do that differently...last one I had used the vac connection on the carb that needed a line connected under the blower to operate correctly...just a thought....Rob

UPDATE:

.010 wire in powervalve passages didn`t stop the fuel dump completely but it helped to keep the AFRs out of the high 10`s at about 11.2@ 4300 I`m good with that. seems to be the same AFR all the way to 5200

me thinks if you go down 1 jet size all the way around,YOU WILL BE GOLDEN!

Dan, the wire installed in the PCVR helped. Leaned the midrange by about .5 from what your saying. (you were 10.8 at 4200 before?) I'd go up another .010 in wire size, then add secondary jet. This should get you in the 11.5 range at 4200, and 11.0 range at full kill. Your just pulling a little fuel from the midrange, and adding some on the big end that way. The .010 size I suggested earlier was just a starting point to see what it would do. I'm not that good to get it spot on for ya! lol

I wouldn't go much leaner at wot. Iron heads, overdriven blower, and no intercooler, its not worth hurting the engines for 1/2 mph gain. Mercury's 600SC, 800SC, 525SC, all ran fat. Probably much fatter than low 11's at wot. They didn't get the best gas mileage, but they also didn't blow up, and you could stand on them all day.

Here is a chart regarding the effect of power when it comes to air/fuel ratio. Granted they did this test on a sbc with a small blower, but generally it coincides from what ive seen on the dyno sheets.

You'll see that going from say 10.5 AFR, to 11.5AFR, you gain about 1% in power output. 1% on a 800HP engine is, well, 8HP. Looking at a couple dyno sheets from my engines, one pull it made 798HP at 6000, AFR was 12.8. Adding 2 jet sizes all around, next pull, it made 794HP at 6000, AFR was 12.2. Keep in mind this was on the dyno, and we left it with the 12.2 AFR jetting. The day we dyno'ed, it was early spring, cold out, and the dyno cell has excellent airflow. In the boat, Im much richer with that jetting.

When we ran it last I was 12.2AFR at 3500 (1psi of boost) this time around its around 12.8. I think a little more primary and a .020 wire might do the trick.
Not too concerned about a few HP, just want the motor to run on healthy