Zenith TIN Proper O-rings Sizes

[VFR750]

The typical Zenith TIN rebuild kit has the wrong size O-rings for the Idle Mixture Screw and the Accelerator Injection Tube. After measuring the hole and shaft sizes, I tried a few ones out and selected the best fit. They worked great.

Here are my results: McMaster Carr sells metric O-rings that fit. They are really cheap.

Idle Mixture Screw : 1.6mm thick by 2.2mm ID
Injection Tube: 2.0mm thick by 3.0mm ID

[BK911]

Nice. Thanks!!

[9112.2t]

Thanks

[ARCSinAK]

Ya stoked for your help!

JS

[al lkosmal]

Great info.....................thx for that. I added it to my ever growing file of Porsche tech docs.

regards,
Al

[rodoredas]

Hi Mike

I'm half way through a complete rebuild of Zeniths as well and having trouble with o-rings in the rebuild kit and have a question about the Air Correction Jets

I have new 34mm Venturis, new 0.5mm Injection tubes, new Idle Jets (55,57), new Idle Mixture screws, new main jets (145, 162,165), new air correction Jets (170,175), new insulation gaskets, new diaphragms and springs etc

1. None of the 4 different o-rings in the rebuild kit seem to fit the Idle Jet properly, which ones have you used? see below

2. Do you have any tips on how to install the o-ring on the Idle Mixture Screw? Have i got the right one, see below

3. the Air Correction Jets that were in the carbies are stamped 210, way larger than your recommendations in other threads

cheers

[VFR750]

I am assuming this is for a 3.0 conversion?

1) the idle jet seals at the very tip of the jet and the threads. I have not used an o-ring to seal it.

2) Yes, they are tough little buggers to get on. Use oil to lubricate it, and roll it on. It's tough on your finger tips.

3) 210 are very large. you will have a very lean top end, too lean. Do not run them. Go with 165s or your 170s.

[rodoredas]

Thanks Mike

yeah this for a 3.0 I got from 911Tweaks a few years back

1) I understand what you say about about the idle jets sealing at the tip, the new ones from Alfa1750 are slightly different to the old ones, do you think it's ok that they fit as shown below where i have pix of the new and old in the body, the old one has a seal, the one is screwed all the way and there i substantial gap, is this what you have seen before?

2) thanks, I'll try harder!

3) ok, I shall reduce

cheers

[VFR750]

My idle jets stick out like that. My old 47.5 idle jets look like new ones too. Never had a seal.

[rodoredas]

ok cheers thanks Mike

[bobolsn]

Thanks for the information on the o-rings. I have "rebuilt" my zeniths a couple of times using the kits. I had the same problem with the o-rings, can't understand why they provide o-rings that don't fit. I reused my old ones (probably not a good idea, but could not find replacements).

Anyway the questions. The carbs were running fine when removed, but have been sitting for many years. I was going to rebuild again with the kits and the proper o-rings. Also, I am interested in what others have done to make the zeniths more responsive or efficient (tighten linkages, new bushings, new springs, polish venturis, etc.). Also, the floats are 40+ years old, are new ones available. I am not sure the floats need replacing, but thought I would ask. The car will be a driver and maybe a DE course.

I have noted references to an individual or two who are highly regarded "experts" with Zeniths. What do they do for a restoration?

TIA

Bob

[rw7810]

it probably doesn't make them anymore efficient, but cleans up the look to remove the side tubes and emission unit. Just plug the three holes and you're good to go.

[VFR750]

Other than cleaning, i did not do any restoration. Hence my idle is a little variable due to air leaks betwee the throttle shafts and the bodies. Plus, i live with the transition stumble due to the port layout. This is well documented.

The experts can restore your carbs to like new condition or better. Performance Oriented, Paul, lists exactly what you get for your money. He can solve the stumble issue too, by changing the transition ports to match a weber IDA.

[rodoredas]

Hi Bob,

I'm no expert in the field and I have gone a bit over the top with the work i'm doing with my Zenith's mainly because I just wanted to learn more about them and have the experience of rebuilding

I've Soda blasted the internals using my own blasting cabinet, soak in water to dissolve the bicarb soda, air dry, was in carby cleaner. Used various cleaning products from petrol to carb cleaners on the rest.

I've purchased:

new 34 mm Venturi from pelican chris_seven (UK)
floats from pelican tom1394racing, he may have more
0.5mm Injection Pipes (standard are 0.3mm i believe) from chris_seven
insulation gasket kit for manifold to engine, consists of normal gasket either side of insulating gasket from chris_seven
various sizes of - idle, air correction, main jets and holders, idle mixture screws, air bypass adjusting screws, pump springs, main jet holders and float level needle valves from ebay Alfa1750 - he's very good , based in Italy
I've used the pelican kits for some gaskets, washers and o-rings but I don't think they are worth it, but did use the diaphragms from these kits
I've removed the auxiliary unit and tapped the holes and vacuum pipes and inserted grub screws.
I've got some flat top filter covers, gaskets and K&N filters from Supertec Performance
Bought fuel regulator, fuel filters from pelican plus a synchrometer, i want to mess with this once i get these going!!
I'm using fuel injection fuel lines as recommended by my local expert porsche mechanic
and taken advice from pelican experts (1QuickS, VFR750) and other threads

Spent a lot of time cleaning and searching and waiting for bits to arrive but it's all good fun. I've done one carby and now that I know what I'm doing and have all the bits the second one should be way quicker and easier.

cheers

[bobolsn]

Shane and VFR750,

Thanks for responding. All I can say is WOW. 90% of your response was over my head, telling me that I have alot to learn. I can do cleaning, but I am not sure what the effects of modifying/restoring/etc the other components has on performance. I will slowly learn.

Is there a book/site that I can read as to what each component controls and there relationship? (air correction, air by-pass, injection pipes, etc.)

I do have the link to the Zenith technical manual. So I guess the first order is to read that and confirm what I don't understand. This will provide me with hopefully a basis to ask the right questions.

Thanks
Bob

[rw7810]

bob - can you share link to manual ??

[bobolsn]

This is the link that works for me. I just went there.

Zenith 40 TIN Carburettor Manual

Bob

[1QuickS]

There are two types of idle mixture screws for the Zeniths and the o-rings are different depending upon which one you have.

[rodoredas]

Paul, that's what I've noticed on mine, the difference between the old mixture screws and the new one's I have from Alfa1750.

Bob, I started with this pdf catalog you can download from the porsche.com, choose 911, 70-73

Genuine Parts Catalogue - Classic Genuine Parts & Literature - Porsche Classic - Dr. Ing. h.c. F. Porsche AG

I also have the workshop manuals which provide a great deal of detail, I'll pdf them over the next day or so and can email it to you - is that infringing some porsche copyright rules, i'm not sure!

cheers

[bobolsn]

Shane,

I downloaded the parts catalog. I had just discovered the Porsche.com web site through this forum, but did not know you could download. It is a BIG plus when you are putting a car back together after many years. I took notes when disassembling, but you know how that goes.

I had been looking for a workshop manual, but the ones I found were for post 1973. My 911T is a 1971, so I need the first 2 manuals.

Bob