I never did run the carb w/pv's before going on the blower so I am starting from scratch.I have a 2.5 pv in now with the guage showing 4/5" vacuum but the idle mix is still in the 12.5 to 13 a/f ratio.I will get back at it tomorrow.

I still have the pv plug in the sec circuit and 88 jets but the pri has 76 and the 2.5pv,32 squirter,orange pump cam 1# hole and just checking things out in the garage it was lean n backfire in the intake/carb.I only have a 4.5 and a 6.5 pv to work with beside the 2.5 but my carb jets are from 76 to 90 and I think factory was 80 with pv's in the pri.The timing is at 32 to start 93 octane.
ps the carb is an 4150 with choke horn no plate in it,factory air bleeds non adj.

Idle has no impact on the p/v unless it's loose or ruptured.......steady state cruise and a couple inches below that will get ya close then pvcr sizing and secondary jetting accordingly.............What list number or size is it...........

My adjustments are so I can get to the driving part so far.I started with a 6.5pv and 80 jet in the pri but the pv gasket leaked and at that point i connected a vac guage and saw the low vac and put in the 2.5 but with 76 jets to keep it from coating the plug with fuel so I have been rich,now lean I can work to the proper tune.Thanks for you interest.

I'd start with a brand new 6.5pv, and 78/88 jets and adjust from there.
This is assuming you're using a 4781/850 carb.

Yes it is a 4781,The 6.5 has been sitting in a tray for 15yrs from when I got the carbs and seems to be ok when put vacuum on it in my mouth.I wont be driving in the rain today but will check the carb over again.Thank you for your help.

If the rubber diaphragm gets stiff it changes the point at which it opens/closes.

They don't have to leak to not work properly.

Holley made many 4781 from the original with no power valve in the secondary to the 4781-9 I think with power valves in both metering blocks, I think my 4781-2 didn't have a power valve in the secondary My 4781-6 came with one size smaller jet in the rear than the primary jets where
What is your - list number ?

Mine is a -8 list.I agree with the age of the pv but with low vacuum don't you think I should use a low #pv?

Get QF 4 window p/v...............

I will check that out thanks.

Is this carb. on a intake now and not on top of the blower?

Yes a Victor 440

I had 83 not 88 in the sec with pv plugged so it should run much better and I will go for a ride in a day or 2.I also put the 78 in the pri side from 76.

A reason the carb is so out of adjustment is I loaned it to a Ford guy to use on his 428 65 Mustang buy it looks like I am headed in the right direction.I had 10" of vacuum with the blower and the same cam so I should be able to get more out of it.

I looked at Holley spec. sheet on their web site, you may want to call them or look yourself to verify that your carb came with #78 in the front and #66 in the rear stock I'm sure it comes with dual power valves like my 4781-7 did

Ya a 66 may be wrong for the rear but I don't use a pv there.Thanks for the info!

The blue pump cam is much better on the 2nd hole, and switch up to 35 squirters should take care of your lean backfire if its a carb related issue.

I think the factory cam will be ok but I do have the 35 in both ends now.

Also only used the blue cam on the primaries. Used the stock cam on the rear, witch I think is the orange cam. The blue cam gives a much bigger immediate shot on take off. Its a very Go to pump cam for these mopar BB race cars on carbs the size of yours. You may be getting one down the road. I also agree with starting out at 78/88 on the jets and tuning from there. Street driven maybe 76/88