Starting Carb Conversion: Flat Tops to Paltechs

[Dadsun 20]

I'm in Louisiana. I would think if I were in Canada the coolant (heating) lines going through the manifold would be more important.  This other topic has several folks voting to keep the lines flowing, however, due to keeping temps from getting too uneven in spots.

 

[siteunseen 3,448 5 Vehicles]

23 hours ago, Patcon said:

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

I can't tell if your pro or con on this. Doesn't matter but being a southerner that phrase could go either way.

 

Edited December 13, 2020 by siteunseen

[Dadsun 20]

I bought this replacement gasket from Z Car Depot. Is it recommended to use a gasket sealant on this?

[DatsunZGuy 129]

2 hours ago, Dadsun said:

I bought this replacement gasket from Z Car Depot. Is it recommended to use a gasket sealant on this?

I recently installed a new manifold gasket and did not use sealant.  No issues experienced here.

 

[7tooZ 187 1 Vehicles]

45 minutes ago, DatsunZGuy said:

 

I agree

[Dadsun 20]

Getting very close to the finish line. 

I sometimes, on projects like these, wake up and think about things I've forgotten... Like whether the throttle linkage arm is the same length on both flat tops and round tops setups. Alas, they are not. :-(. Looks like my flat tops arm is an inch or two short for this project.

My options seem to be to (a) make an extension, or (b) keep looking for one. 

 

In the meantime, here are some pics....

 

Edited January 3 by Dadsun

[Captain Obvious 2,387]

Right. When you switch to the 240 style balance tube, you'll find that your old shepherds hook is too short.

Not the most beautiful thing in the world, but you can cut your original in the middle-ish and weld on a piece of tubing to take up the gap. Here's one from a 74 260 as an example. I believe they changed the pivot mechanism that mounts to the firewall and the shepherds hook design between 73 and 74, so yours won't look like this. But the concept is the same:

Extendo mod used on a 74 that switched to a 240 balance tube:

And here's a pic after the welding is done and cleaned up a little and installed. Note the newer design throttle linkage pivot on the firewall. Seen on the right side of this pic:

So I don't know if the newer design pivot will bolt right up to your firewall, but if it does, you could switch to that and a longer shepherds hook from a 280 or ZX.

[Dadsun 20]

Hmmm. Thanks. I was just assuming the way to go for a non-welder like myself would be to affix an extension of the eyes that receive the shepherds hook. 

[Captain Obvious 2,387]

Many different ways to lengthen the linkage, so whatever works easiest for you.

If you take a good pic of the piece that mounts to the firewall, I'll snap one of the later version. If it looks like the new one will swap over as a bolt-up, I've got one here and a longer shepherds hook that I could part with. You could just bolt that in and go. I'll snap a pic of that if I get a chance and you're interested.

[Dadsun 20]

Yes, interested. Thanks. Here are a couple of pics. It looks to me like the shaft is about 2" to 2.25" short on the new setup.

[Dadsun 20]

Actually, the old flat top setup's receiving rod adds back the two inches. So, I'll insert that and should be stable enough to do the job. See pic:

 

[Captain Obvious 2,387]

That old flat-top part should get you out of the woods for now. It really wants a bearing support closer to the end, but I think it should be OK for now.

So here's what I have. Question is... Will the pivoting mechanism mount to your firewall? Are the mounting holes in the same location(s)?

 

[Dadsun 20]

Wow,.that's nice. And yes, I'm wondering about the support on the carb side with that longer arm. Here is a picture of the underside. Looks like the middle hole is flipped, but the two outer holes line up. 

[Captain Obvious 2,387]

If I get a chance, I'll take another pic today with a tape measure up against the bolt holes so you can see if it's the same as what you currently have.

[Dadsun 20]

Center to center distance on those two mount holes is 1 9/16". 

[Captain Obvious 2,387]

It looks like the newer design will bolt up. I'm kinda surprised.

Here's a pic of the dimensions on what I have:

Send me a PM and we'll see if we can reach an agreeable agreement.   

[Dadsun 20]

Well, the carbs are on, no leaks, and it starts every time. Progress!

Now I need to tune them. I have a Uni-Syn tool that came with the car. I'm getting no air draw on the front carb, just the back. Is that normal?

I have a service manual and saw some old threads here on tuning/balancing, but if y'all have a go-to reference please pass along. 

[siteunseen 3,448 5 Vehicles]

Edit: That looks damn good!

That front one has a nipple on the backside for distributor vacuum advance. Is it open?

Here's what I used to begin a basic tune. Thank you! @240260280

 

 

Edited January 13 by siteunseen

[Dadsun 20]

I have a line from that nipple to the distributor, so I think that's the correct setup. See pic.

[Dadsun 20]

Ok, I'm looking at the Quick and Dirty SU Tuning thread. For balancing it says: "2. Warm up car and remove all linkage connections so that the carb's throttle plates are resting on their set screws.
3. Adjust each set screw so that the suction felt when you put your knuckles against the throat of each carb and feel the air flowing between your fingers is the same on both carbs."

... Is the set screw the same as the throttle adjusting screw on each carb?

Also, my setup came with no screw in this place (next to zip tie in pic) that looks to be opposite the balance screw. The guy who refurbished them said no screw necessary there.

 

[siteunseen 3,448 5 Vehicles]

I think that missing screw is what adjust the throttle plates. As in your 2nd sentence, #13 on the diagram.

I always unhook that top plastic marble to release the linkage during adjusting. Closest to #8.

Here's the spring loaded screw you need. Probably easiest to get one at motorcycle shop. They're on bike carbs.

[Dadsun 20]

So, if I understand that correctly, the missing screw is needed for the air intake balancing work? Argh. 

[siteunseen 3,448 5 Vehicles]

It's been awhile but the airflow sync I use to balance air flow I turned #10 screws on my '72 SUs.

That spring loaded screw you're missing keeps the linkage tight and snug for butterfly respose. It's not really used to balance them but keeps them responsive to your foot on the pedal. 

I would watch a few YouTube videos. There's some pretty good ones now. Good luck.

Edited January 19 by siteunseen

[w3wilkes 237]

Since the #6 Diaphragm (and #3 control valve) has been removed on your car the #13 screw does nothing. The zip tie is just to keep the bar the #6 diaphragm and #13 screw attach to from flopping around since it no longer is used to slightly hold the throttle open during deceleration.

[jfa.series1 822 1 Vehicles]

Here's an alternative view on the function of the missing screw (#13). Its purpose is to adjust/manage the effect of the servo (#6). The servo is an emissions control device to slow the rate of deceleration of the carbs when the accelerator pedal is suddenly lifted and avoid a dump of raw fuel into the intake. That's why the decals on the air filter say "don't touch". With the servo deleted from the balance tube, this screw either missing or present makes no difference. The zip tie on the linkage can be left in place or removed, same answer - no difference.