5 minutes ago, Patcon said:

Can the engine pull the butterflies open? I wouldn't think so

Doubtful. I've seen it sometimes get the butterflies to hang open when the throttle is closed slowly, but if you blip the throttle, they would settle to where they belong.

I would really doubt the vacuum would win a battle against the return springs and actually pull the butterflies open.

When revving the car and dropping the throttle. The mixture goes very lean. Rpm drops to 500-600. Then it recovers back to 1500rpm. Would heavier oil in the dash pots help reduce that? I think they have tranny fluid currently

Heavier oil wouldn't do anything about that. The oil really only has an impact when OPENING the the throttle, not closing it.

But curiously, usually when you close the throttle abruptly, they go very rich, not very lean. Are you really sure you're really lean? I'm thinking that maybe your A/F meter is misleading you... It might be misfiring because it's so rich it won't ignite (and your A/F reads lean because there is unused oxygen in the exhaust stream?).

In any event, that's less of an issue than running lean under steady state conditions. Whether it goes rich or lean on deceleration is a transient condition that isn't as important as what it does when you're driving steady.

Do you have one of those cheapie smoke machines? Use one of those to look for leaks?

8 minutes ago, Captain Obvious said:

Do you have one of those cheapie smoke machines? Use one of those to look for leaks?

It's easy to make a smoke machine, too.

And a slightly nicer way to describe it...

Edited May 2May 2 by SteveJ

I like @Captain Obvious idea of disconnecting the linkage and making sure the carbs are isolated. Hard to imagine restored carbs will not idle low. Is the vacuum thing on the manifold hanging up the linkage? Just a thought.

I pulled all of the carbs and intake today. This is what the butterfly looks like with a really bright light behind it. @Captain Obvious

We loosened the screws and reset the butterfly but it didn't really close up much. The gap is on the top of the bore

10 hours ago, Captain Obvious said:

The oil really only has an impact when OPENING the the throttle, not closing.

10 hours ago, Captain Obvious said:

The oil really only has an impact when OPENING the the throttle, not closing it.

Please explain.

6 hours ago, Patcon said:

I pulled all of the carbs and intake today. This is what the butterfly looks like with a really bright light behind it.

We loosened the screws and reset the butterfly but it didn't really close up much. The gap is on the top of the bore

If you have the idle stop screws turned out far enough that they aren't making contact at all, then I would expect the butterflies to close down further than what I see in your pics. It takes a surprisingly small amount of gap to allow the engine to idle. Are you sure the stop screws aren't holding those carbs open at all? Are you sure there aren't carbon deposits on the butterfly edges or carb body throat preventing those from closing further?

I'll take a pic here of what I would expect on a well aligned butterfly when fully closed. Won't be able to do that tonight, but should be able to get to it tomorrow.

14 minutes ago, Namerow said:

Please explain.

The little jiggly bits on the bottom of the damper stalk form a check valve which is dipped into the carb damper oil. That check valve is provides significant hydraulic restriction when the suction piston is rising (when you are opening the throttle), but it provides way less restriction (because it's a check valve) when the suction piston is lowering, such as when you are decelerating.

Hence, the oil really only has an impact when OPENING the the throttle, not closing it.

Yes, it will have SOME impact in both directions, but the raising direction is way more dramatic than the lowering direction.

So how does damper viscosity affect fuel mixture?

No I believe the screws are all the way backed out. I will check. Can the butterflies be shaped to close better? Without adverse effects...

1 minute ago, Patcon said:

So how does damper viscosity affect fuel mixture?

No I believe the screws are all the way backed out. I will check. Can the butterflies be shaped to close better? Without adverse effects...

Heavier oil = richer mixture.