What are the challenges with using Zenith 40 TIN carburetors on a 1970 914-6 engine?

My understanding is Weber 40 IDTP would be the correct original carb. I also understand that 1970 911T came with this model of Zenith. So in theory, no problem?

We are trying to decide if we should rebuild these Zenith. If they are essentially same fit, form, function as the Weber, we will probably keep them. If there is some domino effect of now that you're using Zenith you also need to replace / modify x, y, and z, then we will probably try to source some Webers.

Thanks for sharing your experiences.

P.S. Would I be correct in understanding that the key concern when evaluating the carbs for rebuild would be:

1. Throttle shaft bearing wear
2. Floats that leak

Parts is the biggest problem. Personally I like them. Not sure but I think Porsche Classic has reproduced some of the parts. You are correct on problem areas.

@DennisV
I know Paul Abbott was working on Zenith modifications and had some rebuild parts

www.PerformanceOriented.com

The TIN40s are essentially "bolt on" compatible with the Webers - throttle linkage, manifolds, air filters etc - but you may have to optimize the jets to run with the 2.0 (if the carbs were from a 2.2) and the modern fuels we have available. Idle and main jet options are easily obtained, but some of the parts can be tough to source. For instance, the eccentric cam roller bearing that activates the acceleration pumps was seized when I got my carbs, and I could not find a source for a new one at the time. So I had some machined up.

Properly rebuilt and set up, they have proven very stable and reliable, FWIW. There's some good online info about setting the floats on reassembly, and of course, check float levels and such like you would a Weber and you should be good to go.

Interesting call on whether to fit "what's on hand" (ie. the Zeniths) or spend the $$ and replace with the correct Webers. If its an original 6 - with values buoyant as they are - it might be worth searching for some Webers and just sending me the Zeniths to use as spares.... ;-)


- Tony

For your viewing pleasure.
https://cosprings.craigslist.org/pts/d/peyt...7511359430.html

No affiliation...

I think the IDT carbs are accurate for a -6
certainly the IDA's could work also... but if spending a bunch of money to buy Webers, then just as well find the correct ones...

brant

If you have an engine and want to try them out before you buy them, I have an extra set I was looking to get rid of. I have a set running on my 2.4 now. This other set was listed here, then went to Canada, then to me. I bought them to diagnose an issue with my current ones, but ultimately was an extra gasket on the intake causing a lean issue.

These were rebuilt and I changed out the throttle springs with new ones as the others, while functional, were not correct. I am also going to buy new squirter jets as these were modified. I buy all my parts from Alfa on ebay.

These are/will be bolt on ready. I can also accommodate the jetting to suit your engine. Let me know if interested.

Besides all that you could send them out to Dave Cheney who took over rebuilding Zeniths from Paul Abbott.

I am still on the fence. The car is an original 914-6. The engine is the correct serial number range, but not the original one that came with our car. If it were all numbers matching I would make the leap for the Webers.

The car is in really great shape, but just rebuilding the engine and transmission are going to be pretty significant bills. It's looking like sourcing IDT Webers could add another ~$4k to the equation. We have Bosch distributor that best I can tell came from a 911S, so I will probably need to replace that another $500?

Guess I will try to evaluate these Zenith and see if they are even worth rebuilding and go from there.

Whats the part number on the Bosch disty? It would be useful for you to know what the build details are on that engine. For instance, if a PO has fitted "S" cams and pistons, then MAYBE they fitted the S disty to match the cam; on the other hand, if its the original "T" cam, then you should probably get that unit recurved / replaced...?

- Tony

On the car is Bosch 0231159002 (black label). Best I can tell, this distributor was only on 68 911S, with the yellow label version being on 67 911S. Open to being corrected on that.

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We tear into the engine in about two weeks. I'll know a lot more after that.

It surely has to be better than my first engine rebuild (356 Super 90). The only thing original on that one was the cam, block, head, and carbs. Everything else was done by a turkey (as Harry Pellow used to say). Roller bearing crank for example. Spent a lot of time sourcing parts to get it back original. It's a numbers matching car, save one door. So I've really stuck to originality on that one. I'll probably be a little less uptight about this one.

I rebuilt mine a few years back with all new parts needed and sourced these from Alfa1750 on ebay ,back then there were some parts they didn't list,but asked a question and they had them in stock...very good to deal with.
Check their current listing and you will find there is very little parts they don't have now as they make and stock more parts as time moves on.
Best to give the carbs a basic clean then make sure you can get them apart first,like any carbs that have been sitting some jets,screws and plugs could be stubborn to remove,and lastly take your time ,think I spend around 20hrs on mine ,well worth it.
My throttle shafts passed inspection ,floats failing ? ,haven't heard these are an issue but replacements are able to be found from Alfa1750 also.
In summary a good carb if setup correctly and IMO you will have a hard time finding the original IDT Webers as they weren't made in large volumes unlike the IDA's,end of the day its your car and your $$$$ ,good luck.
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Dennis

my take on the difference between the Zenith TINs and the Weber IDTPs is the Zeniths were primarily a carb for emissions purposes and the Webers were more performance oriented
The IDTPs were original,so go with those
just my 02c worth

cheers
Dennis

If I decide to go shopping for Weber IDTP, it is more than likely I will find them online and have to purchase them without laying hands on them. What photos can I get, or questions can I ask, to avoid getting a junk pair?

The obvious request would be to see a video of them running on a car, but that seems unlikely if I find them on eBay or The Samba.

Thanks for all the inputs.

It's always a gamble when buying them 2nd hand. I would reach out on Pelican. I know I have seen a few sets from time to time. "Off a recent running engine" is usually a good sign. If they were off a running engine, but have been sitting for years they will most likely need a rebuild, better off then some that are ratted out, but still some work involved. They should look fairly clean in pics. If the label them as having "tight shafts" that is a good indicator they could be ok. Also, most of the ones I have seen for sale are off bigger engines. There will be additional cost associated to swap out jets/vents. Aside from the shafts needing new bushings cleaning out every galley is not to bad of a job in the rebuild process.

I started to hijack my own topic, but can't find a way to delete this post. I'll take it to a new thread.

the zeniths are a pollution carb, but if you have nothing else rebuild and use.

,you made some good points,those throttle roller assemblies are now being supplied by alfa1750 as I checked his site today,I had the same issue and fixed mine like you did.
suggate.co uk has the setup and tuning factory manual,handy to have ,used it to "bench set'' my carbs setting up fuel float level and acc pump delivery .