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1974 1/2 260Z Flat Tops minimal viable connections


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Teflon suit on - Check

Here goes...

Ok, first post here and relatively new Z owner (1.5yrs, 260z 2+2 Auto).  The car has weber 32/36 conversion with all the smog stuff removed. It runs decently well, but is rich at idle and takes a bit of cranking (6+) to start if it sits longer than 2 days.  It doesn't have a lot of power but I don't really know the baseline.  The engine runs smooth, and it definitely pulls ok, but I think it's probably in the 75% range of what it could do if tuned properly.  It has a resonator and catalytic converter and original exhaust manifold. I recently switched to non-ethanol and it seems to like that a little bit more, slightly easier cold-starting, a little less missing and oddness. The engine/exhaust note isn't anything I'd brag about and it's more along the lines of a chill cruiser (partly probably reinforced by the auto transmission). Finally, the webers just don't look right in there and I just really love the original look of the SU's with the orange airbox.  

Sooo... I picked up a few Flat Tops (a NOS front, and a used pair with an airbox) and a refurb kit, thinking I would keep it correct for the year, but without re-configuring all the emissions stuff.  I'm looking for some advice here from folks who have experience with the flat tops and don't hate them but that said, I welcome all feedback.

My basic question:

What's the minimum viable connectivity with the emissions deleted? 

Do they NEED vacuum? 

Do they NEED coolant?

Do they need the temp control stuff and the anti backfire stuff?

Does anyone have or know of good HSM for the 260Z fuel system?  The HSM from Xenon is better than nothing, but the scan quality is so low for the fuel system portion it is hard to read.

Thanks for all comments and feedback, 

-j

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4 hours ago, jb260 said:

Do they NEED vacuum? 

Do they NEED coolant?

Do they need the temp control stuff and the anti backfire stuff?

Does anyone have or know of good HSM for the 260Z fuel system?  The HSM from Xenon is better than nothing, but the scan quality is so low for the fuel system portion it is hard to read.

I'm not sure what you mean by "vacuum". All carbs need vacuum. It's what makes them work.

About the coolant... You can make the system work without coolant running through the carbs.

About the temp control and anti-backfire stuff... You can make the system work without those.

And about the documentation... Search around for the "Fuel System Modification" document for 73 and 74. Has lots of good pics and other carb goodies.

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So, looking at pictures, vids etc, it looks like there's a pressure line (copper?).  In the owner's workshop manual, I don't see it on the sectional view for the HMB 46W but there is a small brass connector sticking up out of a squarish protrusion above the throttle valve plate, and I'm guessing that, based on the removal instructions and the video's I've watched of removal, that is the "distributor vacuum pipe".  If I go through all the items in the owner's workshop manual which are to be disconnected during removed, I see the following:

  1. coolant hose
  2. fuel supply pipes
  3. air bypass hose
  4. distributor vacuum pipe

Thanks for the tips, I'll start digging on those.   I also saw references to additional equipment for Auto Transmission cars but haven't yet found anything in the workshop manual referencing that.

Edited by jb260
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There should be a vacuum line coming up out of the squarish portion of both front and rear carbs. The connection from the front carb controls the distributor vacuum, and the one on the rear carb controls the EGR system. If you're not running EGR, you can do without the one on the rear carb, but the front one most likely has to stay.

And the air bypass hoses are a requirement. They need to stay.

Can you post up a pic of the documentation you are operating from?

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On 9/12/2021 at 11:43 PM, jb260 said:

I'm looking for some advice here from folks who have experience with the flat tops

Just a little, if they are not perfectly restored they change every time, you constantly busy adjusting them till the point you wish you never seen them!

That was 30 years ago, now i think with the right parts you can build new flattops in a way they work well.. but the question is can you get those good parts so to make a good set of flattops?  

Most people hate these ft's because they are a pain to adjust.. roundtops are more easy.. i think, i never bottered to look at ft's .. i make a big bow around them Hahaha...

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