Carburetor Conundrum (260Z)

[Captain Obvious]

Oh, and DadAndLadZ, forgot to mention.... Now that you have that nail pulled out and all the idle screws backed completely out, both carbs should be shutting tight-tight. And if that's the case, it probably won't even idle. You might find that you have to manually hold the throttle open a little bit or screw the idle screws back in some just to get it to run at all.

Or you could pull the choke lever. As you saw, it should open the throttle plates a small amount.

Pretty sure you would have figured that out, but just throwing that out there.

[DadAndLadZ]

Well, we put the carbs back on today and did a rough dial-in and even managed to take Project Z out for a little sprint around the block. 

I have been thinking about what @Captain Obviouswrote the other day regarding where the distributor advance hose goes, and found some pix of SU carbs where the "nail hole" did indeed have a hose nipple on the exterior. I still have the advance hose hooked to the port right behind the carburetor in the manifold for now but I totally see what the Cap'n was talking about. Would something like this (image below) work, if I tapped the hole out a little to thread it in?

Or is there a readymade part for this? Any advice on this is welcomed.

Oh, and I put together a new video for our YouTube channel, too. This one was more fun than the last couple because it felt like we actually made a little progress!

 

Thanks again, folks. Let me know what you think about that vacuum port biz above, if you have an opinion on it. Oh, and also on the overheating! Plz/thx.

 

Best,
MC in Wichita

[Captain Obvious]

Well that sounds like significant progress. I skipped through the video really fast though. I'm not much on videos, especially long ones. Maybe it's just me, but I'd just rather read a couple sentences about it instead of having to watch a 15 minute video about it.   A text synopsis about the video would be better for me.

"We removed the nail. Put the carbs back on the car and the idle was down where it was supposed to be. Now that the carbs were behaving like they should be, we did a quick tune and set the idle speed and sync of the carbs using a uni-sync tool. After that, it was running well enough that we actually took it out on the road for a quick road test. Did great, all things considering."

That would be better for me.  

So about that ported vacuum source for your distributor advance... I'm not sure what you have is salvageable, at least not without extraordinary means. The problem is that the hole into your carb throat is way bigger than it should be. Looks like when they snapped off the vacuum nipple, they drilled out the remains and went too deep. Like all the way into the carb throat deep.

In other words... Some previous owner drilled through your carb body and ruined it. The vacuum hole is supposed to be small. Thirty thousandths maybe? And the one in your carb looks like it's an eighth inch or larger. The bottom line is that both the size of that hole and the location are critical and yours has been wallowed out to three or four times it's normal size.

So if you want to run ported vacuum, you'll need a new front carb. Not a lot of fun.

[siteunseen]

Couldn't he come off the balance tube's locations? Or find the right size brass tube and JB weld it in place on the front carb.

https://www.lowes.com/pd/Hillman-Brass-Plain-Tube/3478161?cm_mmc=shp-_-c-_-prd-_-hdw-_-ggl-_-LIA_HDW_126_Fastening-_-3478161-_-local-_-0-_-0&ds_rl=1286981&gclid=EAIaIQobChMI_o2dusGt-QIVbnxvBB2RTQ_NEAQYASABEgL4ZPD_BwE&gclsrc=aw.ds

[w3wilkes]

It may be that the current vacuum advance from the intake manifold is okay. Should be able to tell how the advance is working that way with a timing light. If it's working okay this way the hole in the carb could just be plugged (with a nail 😁, not really).

[DadAndLadZ]

Just now, w3wilkes said:

It may be that the current vacuum advance from the intake manifold is okay. Should be able to tell how the advance is working that way with a timing light. If it's working okay this way the hole in the carb could just be plugged (with a nail 😁, not really).

I do have a timing light and we will be working on that coming up.

[Captain Obvious]

Here's a couple pics of the 72 carbs (which is what you have in your car) and the vacuum nipple:

And here's the port on the inside. Note that I'm holding the butterfly open a little bit so you can see the hole. With the butterfly all the way closed, the hole is completely covered. Also note how small the hole should be:

 

[Captain Obvious]

Oh, and here's a pic of what the carb mounting surface is supposed to look like. Without the grease lube holes:

[DadAndLadZ]

Just now, Captain Obvious said:

Here's a couple pics of the 72 carbs (which is what you have in your car) and the vacuum nipple:

Thanks, that is very helpful!

[Captain Obvious]

Glad to help.

So for the vacuum advance thing... The ported vacuum will have a sharp narrow peak just above idle. At idle, there will be very little advance, and above light cruise, there will also be very little advance.

In contrast, the direct manifold vacuum will be highest at idle and gradually drop from there to zero advance at WOT. The profile is very different than the ported source.

That said, there are plenty of people who think that direct manifold vacuum is actually better, and plenty of other people who think that all the vacuum advance can be removed completely and just set the base timing higher instead.

Here's a discussion we had a long time ago about such things. Quickly went over my head:
https://www.classiczcars.com/forums/topic/41935-ignition-timing-theory-port-source-vs-manifold-source/#comment-377416

 

[DadAndLadZ]

2 minutes ago, Captain Obvious said:

Here's a discussion we had a long time ago about such things. Quickly went over my head:
 

 

Oh this is very useful! Thanks! 

[Racer X]

On 7/7/2022 at 1:13 PM, SteveJ said:

By the way, if you haven't done so already, go to https://www.classiczcars.com/files/ and download the factory service manual for the 260Z. Yes, your car has been modified, but the FSM will help you identify how it looked from the factory.

I would also suggest getting the FSM for an earlier Z, say the 72, to compare the setup for the earlier round top carbs.