Carb/power valve settings for a 4.3L V6!

[loco]

No Title

That's some mixed information! I've gone for the white spring for now, will swap to the red if it is opening too soon.
Holley got back to me with a chart of spring rates, attached!

The low vacuum is a concern. I'll investigate.

 

[Scott Danforth]

most of the holley specs for VP marine engines used the white spring, hence the reason I use the white spring.

The black spring wouldnt open the secondaries fully ever, not an a 350, not on a 252 (4.3)

 

[Lou C]

However at idle vaccum should be higher due to it idling with no load and it should be more steady as well; the idle instability shows that

 

[loco]

I read you can use gas (e.g. Butane) to find a leak. I'm thinking of using an unlit blowtorch, and moving it around the intake area.
Would the instability suggest the leak was isolated to a particular cylinder or so? I.e., if the leak was around the carb mounting plate, it would be low, but static, but if it's one cylinder, then vacuum would be lower when that cylinder should be drawing in air, so the reading would fluctuate?

I guess swapping out the inlet manifold gasket is dead easy, and I could add some sealant when I next fit the carb, and see how that goes. After that, I guess it gets more serious, with valve seals, low cylinder compression, etc.

 

[Lou C]

Prop safer to use motor oil squirted around the intake gaskets and carb gasket and see if your vac gauge temporily shows a higher reading. Use a low Vis oil like a 5/20. Replacing the intake gaskets looks easy but I just pulled mine off and trust me at least the non Vortec gaskets get stuck on like cement. Not at all easy to remove. The heads by comparison were much easier to remove....

 

[loco]

Had a half decent result - I plugged the left hand Rocker cover vent, and blew in the right hand pipe (with engine off!), and could hear air escaping from the sealant between the manifold and block. I had my torque wrench with me, so re-torqued everything, and it was all loose. After tightening, no air leak, and the idle went steady and up to around 17in/hg! Happy days.
Video here, but the audio just captures the noise of my PS pump which has given up on life. You can see that very little in the way of fumes come out of the blow-by vent at idle:
https://youtu.be/Zzdni3asznQ

With no PS pump, I can't test the secondaries, sonwill approach that once the new unit comes down.

Thanks, all.