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Jetting Zeniths
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fichri
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PostPosted: Fri Jun 04, 2021 6:14 am    Post subject: Jetting Zeniths Reply with quote

Hello, my name is Philipp from Switzerland.

I would like to realize a project. I have a 1200 cc engine with 2 Zenith 32 ndix and 24mm Vernturis on WW Okrasa cylinder heads. My question now is how do I jet the Zeniths for an optimal run. Does anyone have an answer or experience?

P.s. does the standard fuel pump have enough capacity to supply the 2 Zeniths?

Thanks and greetings
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5500
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PostPosted: Sat Jun 05, 2021 7:13 am    Post subject: Re: Jetting Zeniths Reply with quote

Hello Philipp.

Using the standard jetting for a 1600 "Normal" (60 hp) Porsche will get you very close. 356carburetorrescue.com and derwhites356literature.com contain a wealth of information about 32 NDIXs, but I haven't found a definitive answer about specific jetting for vintage VW engines beyond using the 356 normal as a starting point.

Most of the "boutique" fuel pump restorers recommend installing a 356 diaphragm spring to boost the pressure but it doesn't sound absolutely necessary. From what I've read, the Zeniths do not require a lot of pressure.

Also, you may want to try contacting big E deluxe on this website (and check out his awesome 1958 outlaw beetle build thread in the vintage speed section here). He is running Zeniths on a 1397 vintage motor. I haven't seen specific information about his jetting but he is responsive to many questions in his thread.

I am waiting to get my carbs back from restoration to finish my 1397 install. When I have more specific information, I will post it.

Good luck!
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Big_E_Deluxe
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PostPosted: Wed Jun 09, 2021 8:04 am    Post subject: Re: Jetting Zeniths Reply with quote

Hey phillipp, I agree with 5500. 356carburatorsrescue.com has some great info on the NDIX.


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I'm using the "Normal" setup with 24mm venturi on my 1397cc. Engine runs well, smooth power. I have not tried any of the other combinations as of yet. I need to pull the carbs to solve a small leak soon and may try looking at a different combination....maybe.

As far as fuel pump, I'm running an early Porsche 356A fuel pump, tested @ 2.5 psi. Hard to tell if it's necessary or not. But I can say that I'm not having any issues. I'm not an expert on the ins and outs of these carbs, so I'm not sure how much tweaking can or needs to be done. I hope to find someone with NDIX knowledge locally to further tune this engine. An engine stand dyno would be the best way.

They are great little carbs and seem to be a good match for this size of engine... Good luck!


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Erik

1958 VW Beetle - "Max": https://www.thesamba.com/vw/forum/viewtopic.php?t=...highlight=
1959 VW Bus - "Hans" - Double Door Panel (sold): https://www.thesamba.com/vw/forum/viewtopic.php?t=746927
2014 Porsche 991.1 Carrera S
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fichri
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PostPosted: Mon Jun 14, 2021 1:02 am    Post subject: Re: Jetting Zeniths Reply with quote

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Hello everyone, thank you for your information about Zenith jetting. It really is the case that the Porsche 1600 jetting works very well. The engine is a 1200, original crankshaft and camshaft with 1:25 rocker arms. WW "Okrasa" cylinder heads and SG manifolds. Linkage is modified from the WW kit. The engine feels like 48-50 hp and runs really well from 3000 to 5000 rpm.
The original fuel pump is completely sufficient for the two zeniths
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consvws
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PostPosted: Mon Jun 14, 2021 12:11 pm    Post subject: Re: Jetting Zeniths Reply with quote

My '59 1600cc 356 industrial engine had the single Zenith carb. Only difference in the jets were the air correction jets, they are 180s instead of 220s. I've since converted to dual Zeniths, and found another matching carb with 180 jets. Once I get the linkage all setup I'll test this setup. I might end up needing another pair of 220s to make the engine better for street use. I'm guessing the smaller jets worked better for the industrial application.
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johnnyvw164
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PostPosted: Mon Jun 14, 2021 4:43 pm    Post subject: Re: Jetting Zeniths Reply with quote

At one point in time I had two huge compartment boxes with all sorts of jets etc for zeniths. Alas, 35 years and many moves later, all I have is the carbs, manifolds, and linkage. No clue what happened to the boxes...
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5500
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PostPosted: Tue Jun 15, 2021 4:12 pm    Post subject: Re: Jetting Zeniths Reply with quote

Phillip, thats good to hear. Like your setup!

Eric, are you "maybe" thinking of the 40 PIIs?

Johnny, glad to hear I'm not the only one with missing boxes of stuff after many years of collecting and multiple moves!
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Big_E_Deluxe
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PostPosted: Wed Jun 16, 2021 8:54 am    Post subject: Re: Jetting Zeniths Reply with quote

5500 wrote:


Eric, are you "maybe" thinking of the 40 PIIs?



No, sticking with NDIX's. My 40 P-II's are now in my brother's hands. He has a 356B that he is restoring.
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1958 VW Beetle - "Max": https://www.thesamba.com/vw/forum/viewtopic.php?t=...highlight=
1959 VW Bus - "Hans" - Double Door Panel (sold): https://www.thesamba.com/vw/forum/viewtopic.php?t=746927
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JeeWee
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PostPosted: Fri Jun 25, 2021 8:59 am    Post subject: Re: Jetting Zeniths Reply with quote

there is only one way to correctly do the jetting, and that is on a rolling road / dyno and check the mixture... I can give you my setup however it could not be the right setup for your motor.

By the way, after investing a lot of money to get a few pony's from a 36hp this cost should be peanuts and you will know the power output as well.
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5500
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PostPosted: Sun Jun 27, 2021 1:07 pm    Post subject: Re: Jetting Zeniths Reply with quote

JeeWee wrote:
there is only one way to correctly do the jetting, and that is on a rolling road / dyno and check the mixture... I can give you my setup however it could not be the right setup for your motor.

By the way, after investing a lot of money to get a few pony's from a 36hp this cost should be peanuts and you will know the power output as well.


JeeWEE, do you have before/after dyno charts or numbers to illustrate what you gained (and where in the curve)? What did you do for O2 readings? After you dyno tuned the carbs, did you make any ignition timing changes?
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