Carburetor Conundrum (260Z)

[SteveJ]

22 minutes ago, DadAndLadZ said:

Here is a short video showing the fuel lines: 

 

The capped off hard line is the return to the tank.

The smaller hard line is the tank vent. In stock configuration, it would go to a carbon cannister.

The plastic bottle is the vacuum reservoir for the AC. My guess is that the AC has been removed.

You may want to consider re-routing the fuel line. It will pick up a lot of heat hanging out over the engine. Of course, the stock fuel rail could pick up plenty of heat from the exhaust manifold.

Here's how I routed the fuel lines after I converted the carburetors into throttle bodies.

 

[SteveJ]

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.

[DadAndLadZ]

14 minutes ago, SteveJ said:

The capped off hard line is the return to the tank. ...

 

 

Yeah, I don't like having the fuel line right over the top either, will def move it before this is all said and done. 

I unhooked the choke cables on both sides and removed the spring recommended by @w3wilkes. Here I have both throttle screws backed all the way out and it's idling...check out the difference between front and back when I choke them individually...

 

[w3wilkes]

From your video I don't see that the front choke is also opening the butterfly in the carb. The rear looks to be working correctly. In the snip I stole from your video when you press up on the choke the "bell crank" (1) should be opening the throttle butterfly plate by pushing up on the "L" (2) but I don't see that happening like I do see it happening on the rear carb.

[DadAndLadZ]

4 minutes ago, w3wilkes said:

From your video I don't see that the front choke is also opening the butterfly in the carb. The rear looks to be working correctly. In the snip I stole from your video when you press up on the choke the "bell crank" (1) should be opening the throttle butterfly plate by pushing up on the "L" (2) but I don't see that happening like I do see it happening on the rear carb.

 

Well, I bet that makes a difference! Will investigate, thanks!

[w3wilkes]

Just decided I have another question regarding the "L" (2) thing in my earlier snip. When you advance the throttle (push on the gas pedal) does it operate the "L" pushing it up to open the butterfly plate in the carb? It should!

[Captain Obvious]

So here is an annotated pic showing what I was talking about above:

 

[Captain Obvious]

And just to make sure we are talking about the same screws... You're saying you loosened up four screws (including these) a whole bunch and you are still idling at 2500 RPM?

Edited July 8, 2022 by Captain Obvious

[DadAndLadZ]

On 7/7/2022 at 9:33 PM, Captain Obvious said:

So here is an annotated pic showing what I was talking about above:
 

 

I took the spring off, and I do know that the throttle linkage between the two carbs is loose; I loosened both those as directed by all the various manuals when I started trying to individually balance the carbs. It's not cross threaded, it's just screwed all the way out. I will put a lockwasher on the back one, thanks for pointing that out.

And more pertinently, yes, I can back the idle speed screw on the front carb all the way out and it's still roaring.

It is like 100+ degrees every day here at present, and I also hurt my arm/shoulder over the weekend, so it's likely to be at least a few more days before we get back out to the garage, but I will holler back here as soon as we do. THANKS so much for all the help so far.

[Mark Maras]

2 hours ago, DadAndLadZ said:

 

And more pertinently, yes, I can back the idle speed screw on the front carb all the way out and it's still roaring.

 

 If there are no vacuum leaks, something is keeping the front carb butterfly from closing. I'd remove the domes and pistons from both carbs. With the pistons removed you'll be able to see the butterflies and make a comparison test and perhaps find why it's not closing like the rear carb.

[DadAndLadZ]

12 minutes ago, Mark Maras said:

 If there are no vacuum leaks, something is keeping the front carb butterfly from closing. I'd remove the domes and pistons from both carbs. With the pistons removed you'll be able to see the butterflies and make a comparison test and perhaps find why it's not closing like the rear carb.

Thanks, I had them off before but didn’t know that’s what I was looking for so didn’t take note. I am glad there is a way to check this without removing the carb altogether… This is the one real drawback to these sidedraft units…you can’t see down em! Much obliged.

[Captain Obvious]

Yeah, I was thinking the same thing about the butterflys. It sounds like the front one is not closing all the way. Either due to an external linkage issue, or from an internal issue like the butterfly plate has been removed in the past and was not reinstalled correctly.

3 hours ago, DadAndLadZ said:

I do know that the throttle linkage between the two carbs is loose; I loosened both those as directed by all the various manuals when I started trying to individually balance the carbs.

And I'm not sure what manual you were looking at that recommended loosening those nuts, but it's neither necessary, nor a good idea. I'd get those tightened back up.

I'm thinking it was a misinterpretation of the procedures. Something like maybe you read "loosen the linkage between the two carbs" and your interpretation was to loosen those two nuts?  If that's the case, then it was a misinterpretation, and you should get those tightened back up.