Starting Carb Conversion: Flat Tops to Paltechs

[Dadsun 38]

I bought this Z (1973 240z, white/red, build date 10/1972) in April from the original owner, and have been working on restoring. (Will post some interior pics soon, hopefully.)  As some of you know, like @Captain Obvious and others, the original flat tops were neglected and this car has been driven about 5K at most, in the last 20+ years.

So, after some input from the board, and looking around, I settled on the Paltech round top SU carbs.  They are beautiful.  In fact, I'll have to clean/polish/replace the rest of the engine compartment elements to keep them from looking crappy by comparison.

I an not a mechanic, but consider myself handy.  I need some help on where to start.  See pics.

Q1:  I know where several of these Paltech hookups map to on my ''73, but not all of them.

Q2: I'm assuming the whole EGR crap can go away now - i.e., the wiring, coming from the distributor to the EGR mechanisms. Any tricks/concerns in the process?

Q3: I've read on the forum that certain '72 models have water ports on the mounting between the carbs and the manifold. I have not taken mine off yet, but I'm assuming it will be obvious.

Q4: Any other gotches, must-do's, don't forgets greatly appreciated!

 

[SteveJ 1,253]

1&6 fuel in

2&7 float vents to air cleaner

3&5 coolant lines

4 vacuum line to brake booster

8 positive crankcase ventilation

Edited October 24, 2020 by SteveJ
fixed a goof

[Captain Obvious 2,537]

Wow. Shiny.

Yes, all the EGR stuff can go away. Not that it matters to the discussion, but the control for the EGR doesn't actually come from the distributor. It comes from a relay mounted to the front right engine compartment, under the coil (I think). But whatever.  Haha!

You don't currently have any water passages between the carbs and the manifolds. And you still won't after you put the new stuff on. They're four screw round tops and there are no water passages through the carb faces.

I'm sure there will be some small gotchas along the way, but let's deal with them as they come up.

[Dadsun 38]

Thanks, guys. I believe, as an aside, I could also do away with the ugly heat wrap on the fuel rail now that I'm going to the round tops with the heat shield, carb/manifold spacers blocks, etc?

I've seen posts about going to piano wire for the choke cables, but for now I'm going to keep these and keep applying cable lubricant. Seems to be helping. 

Edited October 25, 2020 by Dadsun

[Captain Obvious 2,537]

Forgot. Your mention of the choke cables reminds me...

Unless they are loose in the box somewhere, you don't have the clamps that fasten the ends of the choke cables on the round tops. The flat top clamps are different and won't transfer over.

Edit - Found a pic. They look like this:

Edited October 25, 2020 by Captain Obvious

[Patcon 2,019]

That why heat wrap is asbestos!!

Proceed with caution...

[DatsunZGuy 137]

Maybe it's the angle or the gasket...but the carburetor spacer look like it's sagging a little in the middle.  Hopefully it isn't cracked.

 

[Captain Obvious 2,537]

I've seen many spacers with that sag. Probably just a shrinkage phenomenon from the molding process.

[CanTechZ 394]

That sag is on all four sides of four screw carb isolators.  I believe it was intentional as the sag looks the same on all four. Three screw carb isolators are flat on three sides and a different shape on the bottom for the water passage.

[jfa.series1 890]

13 hours ago, Dadsun said:

Thanks, guys. I believe, as an aside, I could also do away with the ugly heat wrap on the fuel rail now that I'm going to the round tops with the heat shield, carb/manifold spacers blocks, etc?

First, let me comment that those carbs and manifolds are true automotive jewelry - absolutely stunning!

Your mention of the fuel rail caught my attention so here are a few observations. The supply nozzle positions for the flat-tops are substantially different than for round-tops so I recommend you get a fuel rail from a '70-72 model car - the pic is a Series 2 style from the later '71's and 72's. The rail is longer and correctly positions the nozzles for the feed to the floats. As @Patcon mentioned, the asbestos wrap is a big caution. They put it on the '72's and later, carbed and injected. It has an adhesive that will have melted around everything, expect to find significant corrosion under it. Also, the wrap contributes to deterioration of the nylon insulators for the mounting tangs. I've restored quite a few of these rails and faced all of these issues.

Jim

[jfa.series1 890]

Restored '73 flat-top rail for comparison.

[Dadsun 38]

I'd like to move to a round top fuel rail at some point. Sounds like it's not on the critical path at the moment, but would be ideal.  I've already taken off my flat top rails once and re-wrapped them with new heat shield foil wrap when I was restoring the gas tank and cleaning all of the fuel lines.  I didn't realize the old dilapidated wrap was asbestos. Ugh.

I've texted the Paltech guy to see if he has choke cable brackets.  They were not in the box. 😞  

[Dadsun 38]

An update... I've acquired the choke cable clamps, and removed the EGR housing at the top of the manifold. I am trying to sort out the differences in the flat tops hookups and round tops. 

Q1: Are there any other connections I should be expecting besides the 8 noted above (plus 2 choke cables and the 1 throttle arm)?  [Edit: I also found the small distributor vacuum capsule line hookup]

Q2: Coolant lines: It looks like the flat tops had four (4) coolant line connections and the round tops just the two (2) noted above, so I will need to cap/swap out a couple of connectors coming off the coolant lines to the new carbs. Any tips or links to parts that you've needed? See pics of the 4 current connections:

Q3: Two (2) EGR wires run off into a bundle and I'm looking for the relay.  I'm assuming I can just snip them and wrap them off instead of removing the relay?

Q4: See air filter housing back.  I know that #1 and #2 are the lines to float vents.  And #3 connects to the hose to top of valve cover.  What are #4 and #5?  #4 looks like it takes my breather housing rubber plug (currently sitting on #3).

Thanks for any help!

Edited November 27, 2020 by Dadsun

[Freez74 26]

4 is for air pump.

[jfa.series1 890]

#5 is for a line from the Vapor Flow Valve (see pic). It is a small valve/manifold mounted under the ballast resistor. Fumes from the gas tank and the crankcase are sent to the carbs for combustion.

[jfa.series1 890]

BTW - if you don't use an air pump, you want to cap #4 and avoid unfiltered air into the carbs. A 1" chair leg cap from a big box store is a perfect fit.

[Dadsun 38]

I found the free hanging vapor flow valve hose that goes to #5. See pic. It is in the blue zip tie. Thanks. Sigh, so many hoses to replace.

The other hose within the blue zip tie goes to the crankcase and it looks like the big port there is where my PCV hose from carb linkage is, according to diagram I found, supposed to connect? It is currently not connected to anything. The flat tops setup I inherited had the PCV hose going straight to the air cleaner housing.

Also, I've been reading about wrapping my headers, since they'll be exposed, and some even wrap the heat shield to prevent percolating in the carbs. Any thoughts on this?

[siteunseen 3,753]

I have my pvc to the block and the balance tube as shown here. What kind of headers? Mine are heat coated already and do not get hot at all. The carbs are actually cool to the touch, more on top though.

 

Edited November 27, 2020 by siteunseen

[siteunseen 3,753]

I'll say something on percolation that will get some disagreements I'm positive. I've never had, heard of actual heat problems. It always ends up being something else. Low float bowl levels more than anything. The guys that race use electric pumps to keep the fuel flowing and cool through the return line. 

We've all read about heat causing problems, ad nauseam to the extreme.

 Wrapped headers, youtube heat shields, electric fans and more. Wound up being low fuel level.

[Dadsun 38]

@siteunseen - thanks.  I have no background knowledge here, so it's good to hear that.  I have thought about taking the headers off (they are the standard 3-2-1, which are stock headers, as far as I know) and sending them to get Jet Hot coated instead of wrapping.  But, that's like $400. I just figured if some see it as a problem then now is the time to address it.

But, if the braintrust on this forum think no wrap or coating is necessary, then that's good to know. I have an electric fuel pump back just off the gas tank.

 

[Dadsun 38]

I went ahead, since my header was rusty and fugly, and shipped it off to Jet-Hot in OKC. Two week turnaround. $225 plus one way shipping. 

In the meantime, I'm going through hoses and coolant lines. See pics. What is this inline valve in the coolant line near the break booster (where it connects to a hose that runs around under air filter housing to thermostat)?

[Patcon 2,019]

I believe that is the thermostat for the carb water. If it works its a rare part for those wanting to run flat tops

[Dadsun 38]

Ok. So I can take it out. Btw, Do people sometimes just cap off the intake coolant lines on the round top setups? Talked to a guy in a Datsun shop in Georgia who said it's common. As for now, I plan to run the coolant through the intake manifold. 

[Patcon 2,019]

Maybe somebody else will confirm. I wouldn't think twice about deleting manifold heating

[siteunseen 3,753]

I plugged mine off. Car runs great. The carbs are cool to the touch now. The thing is most of those thermostats fail to close up when heated allowing the hot coolant to run through constantly. Plus you remove potential leak spots. That 90 degree hose at the rear of the head is suspect #1.