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Dadsun

'73 240z flat top carbs dilemma

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Posted (edited)

Hi, all. I'm new to the Z community, but apparently jumped in with both feet... My first Z car is in that narrow range of '73 240z that has the original flat top carbs. Bought this from the original owner a couple of weeks ago. 

My dilemma:

As a newbie, do I try to sort out the flat top tuning and ongoing babysitting (as I've been told to expect), or do I opt for:

Option 2: ZTherapy carbs conversion to their $1300 "bulletproof" modified round tops. Pricey but probably the best long term option to keep close to original. 

Option 3: Weber DGVs in the $800+ range. Heard very mixed things. 

As for me, I'm pretty handy, but never had to tune a carb before. I've watched a YouTube on the flat tops. I'm game if I can get and stay on top of them, but if I truly have to continually tune them long-term then no thanks. 

Edited by Dadsun

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If your goal is to be true to originality, option 1 is the way to go.   A long time member who lives close to me spent the time about 3 years ago restoring and sorting a set of flat tops for his 73.  He has had no issues since as far as I know and has no regrets on the move.   Maybe he will chime in  @Zup

Option 2 is of course the easy solution and can be done for much less is you source a roundtop set for Ztherepy to rebuild.

Option 3 will not get much support from members here.  The side draft webers are a totally different story.

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Welcome, If you restore the flattops to a new state i think just ones doing a tune-up should work.. Investigate if you can get al the new rubber parts etc. to restore them properly..  Tuning these flats is a bit more labour intensive but once done the right way (service manual!) it should work well... i think.. ? 

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I like option 1 as well...of course.  Here is a thread that I blogged during a Flat top resto.  I like the flat tops for the rarity and the fact that they are original to the car.  

 

 

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A couple of pics showing what I'm inheriting. Build date is 10/72.

IMG_20200504_115216.jpg

IMG_20200504_115152.jpg

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I drove a '73 with flat tops for about 20 years until it rusted to death. I found the flat tops to be very reliable and required little to no attention. Once tuned they will just keep going.

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Well, y'all are giving me some encouragement to try to hang with them. Not to mention the Z therapy prices are steep. 

@motorman7, I'll set aside time to read through that long thread of yours. 

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2 hours ago, Dadsun said:

Well, y'all are giving me some encouragement to try to hang with them. Not to mention the Z therapy prices are steep. 

@motorman7, I'll set aside time to read through that long thread of yours. 

Hey some good feed back. As mentioned earlier I didn’t think you would get any positive response to the down draft dual Weber idea.  As I said earlier Keep the carbs you have if you feel like they working okay. Drive that car and learn it idiosyncrasies and study the knowledge of those here here are familiar with them.  The easy route is to immediately go to the Ztherapy route. I will be interested in your updates on the gas tank refurbish.  Good luck any enjoy the process 

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2 minutes ago, Dadsun said:

Am I getting too ambitious if I swap out the K&N for a pair of these in the process?

Yes. For now. Get it running reasonably well before you go trying stuff like that.

I'm not ready to talk you through modifying where you get clean air for your idle mixture air, or what to do with all the other stuff like the idle compensator and the anti-backfire valve and the air pump supply, and the, and the.....

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Ok.  While I'm here, and speaking of fuel, my 240z has no mechanical fuel pump under the hood.  Just an added electric fuel pump back by the tank.  The previous owner has a fuel filter just prior to the electric fuel pump, and again under the hood.  What am I missing with not having that mechanical fuel pump?  When it's cold, I have to turn the key until the electric fuel pump kicks in, and count to 12, then it will usually crank.  Once it's warm, it cranks right up, although I know the carbs need some love.

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Oh come on......

I know some stuff, but I'm not comfortable with that responsibility.   ROFL  Haha!!

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4 minutes ago, Dadsun said:

What am I missing with not having that mechanical fuel pump?  When it's cold, I have to turn the key until the electric fuel pump kicks in, and count to 12, then it will usually crank.  Once it's warm, it cranks right up, although I know the carbs need some love.

An appropriately sized electric being the only pump is just fine as long as it a) can keep up with fuel demand, and b) doesn't have such a high output pressure as to overpower the float needle valves.

But about the cranking thing.... You should enough fuel in the float bowls to run the engine for maybe thirty seconds with no fuel pump at all. If your bowls are emptying out overnight or something, you need to put looking into that on your list.

You've got sight glasses on the side of your flat tops to check the bowl level.

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I've checked the sight glasses.  For one of them (the rear) the fuel level is pretty much always sitting in the middle of the sight window.  The front one, OTOH, is like 20% up the window.  I figure at a minimum I need to figure out how to adjust the float on the front one.  I also need to validate that my choke is closing when i think it's closing.  Those are the two things I plan to do first, besides repair/restore my fuel tank.  Looks like people get good results with the standard POR15 repair kit?

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Posted (edited)
12 minutes ago, Captain Obvious said:

An appropriately sized electric being the only pump is just fine as long as it a) can keep up with fuel demand, and b) doesn't have such a high output pressure as to overpower the float needle valves.

I bought a fuel pressure regulator with a 1-6 lb range, but have not yet put it on. 

Edited by Dadsun

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From the looks of your engine bay it looks like it has all the dealer mods (the electric fuel pump is part of those dealer mods) attempting to eliminate the vapor locking issue (I think ceramic headers could also help with reducing the under hood temp). Are you staying stock or do you plan on any mods like air injection delete, this would happen with the ceramic headers.

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1 hour ago, w3wilkes said:

From the looks of your engine bay it looks like it has all the dealer mods (the electric fuel pump is part of those dealer mods) attempting to eliminate the vapor locking issue (I think ceramic headers could also help with reducing the under hood temp). Are you staying stock or do you plan on any mods like air injection delete, this would happen with the ceramic headers.

To be honest, I am new to the Z car world and figuring it out as I go. I see new issues every day. I would like to stay stock where reasonable, but I also want to get this car on the road and enjoy it.  Right now, I know I have to get the gas tank taken care of, the suspension completely updated, and figure out some basic tuning of the carbs. 

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If you've got fuel at the middle of the rear sight glass and 20% up on the front, then you'll eventually need to take a look at the front. You've got bigger fish to fry right now though. That level discrepancy won't prevent it from starting.

When you get a chance, can you take a pic of the front side of the front carb (the sight glass side) so we can see what type of flat top you're dealing with?

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One thing I saw in your previous pics was that your "choke pull off" actuators are disconnected. I'm assuming the vacuum sources for those have been adequately capped off? If not, that's a problem.

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2 hours ago, Captain Obvious said:

One thing I saw in your previous pics was that your "choke pull off" actuators are disconnected. I'm assuming the vacuum sources for those have been adequately capped off? If not, that's a problem.

I have no idea.  Feeling a bit overwhelmed on where to start. Here's a few pics of that front carb as requested.

 

front-carb-pic1.jpg

front-carb-pic2.jpg

front-carb-pic3.jpg

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Wow. OK... Well after seeing your pics, I think those are the earliest versions of the flat tops. What's your build date stamp on the door jamb plate? Early 73 probably?

From what I've heard, many of those really early ones were pulled off and replaced with later versions because of complaints. And if the customer returned again with additional complaints, then the whole rack was pulled off and replaced with round tops.

In addition to the very early nature of that set, I also see a number of little things wrong or missing.

So honestly... You guys won't hear me saying this much, but unless it's a labor of love and you just want to be able to honestly say "I'm running the original carbs that came on this car from the factory", then even I would change those out.

At a minimum, if you want to stick with flat-tops, I would change over to the later version. If you're not that interested in fighting the incoming tide of sentiment against the flat-tops, then I would switch over to a pair of round tops. Nobody would hate you for that, and in fact, most people would think it's right thing to do.

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Thanks for the honest feedback. The build date appears to be 10/72. 

So, next question is, do I wait it out for the Ztherapy round tops? (They are saying August at earliest) or pick up some at places like this:

ZCarDepot

Or new/used on eBay? Where are the best bets to source them?

 

 

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