FIAT 128 1971

SIMONE128

Low Mileage
Hello I'm Simone from Italy.
I bought a 128 in september and I'm restoring it
The body has already been done, now I'm working on the engine.
I would like to change the carburator but I dont' know if a weber 36dcnf will fit wthout any problem
Do you know if the intake manifold of the 128 rally is ok for the 36dcnf ??
 
Hello Simone,
No, there will be problems - the DCNF does not bolt onto the 128 manifold.
You can solve that problem by installing an adaptor to the existing intake manifold. Or, you can install an aftermarket intake manifold designed to mount the DCNF. If you do either of those things the other "problems" will be smaller. You'll need to modify the throttle linkage, figure out fuel lines, and get an air cleaner that fits the DCNF. But once you solve the problems it should work fine. :)
 
Agree with Mike. You can get an intake manifold to fit the 36. Once you do, its a great carb for the car, and would be very happy with a slightly more aggressive cam as well. That and a bit more free flow on exhaust will wake that car up in a big way.
 
The base "pattern" of a DMTR and a DCNF style carb are very close, but they are not the same. I have seen people "elongate" the holes in the base of the carb to make it fit, or the use of "wobble" type studs, or a simple adaptor plate to mount a DCNF style carb to an DMTR style manifold, but none of these solutions are even close to ideal for a street car.

While orienting a DCNF style carb "sideways" so the throttle shaft is at right angles to the crank axis could work OK for a race application where you're at Wide Open Throttle (WOT) most of the time and idle running isn't a consideration, that's simply not the case for a street driven car, and the "sideways" orientation is far from ideal from a running mixture distribution and also idle mixture distribution perspective.

Early aftermarket manifolds that were available in Italy in the late 1960's and very early 1970's used a DCD style carburettor, that mounts with the throttle shafts at right angles to the crank axis, but on the 36/36DCD the throttle shafts are geared together and the throttle blades tip inwards towards the centre of the manifold opening. You can still find these manifolds around used as the base pattern for the DCD style carb is again different to dcnf carbs, so they are a bit of an orphan, as the 36/36DCD is kind of difficult to find these days, and usually quite expensive if you do.
DCD to 128.jpg

DCD to 128a.jpg

DCD128manifold.jpg
DCD128manifolda.jpg



IAVA in Argentina went a very similar route in their IAVA 1300, using a solex carb that is basically like the 36/36DCD, The IAVA 1300 was the most powerful production version of the sohc 1300 with 99hp at the crankshaft

iava solex carb.jpg

iava_5.jpg

fiat-128-europa-iava-1300tv.jpg


Notice the common theme here? The orientation of the carb on the manifold, this is for even fuel distribution at idle and progression.

Notice the mixture screws for each cylinder are to the "sides" of the carb so both idle jets and progression holes have a chance of providing even mixture distribution to all four cylinders.... if you mount a DCNF style carb to the original dmtr manifold the mixture screws end up in very poor positions for even fuel distribution, they will be both off to one side, as do the progression ports in the throats... so you end up with the problem of some cylinders running much leaner than others during the idle and progression phases.

so sure you can try and reinvent the wheel and mount a DCNF sideways, but you'll run into tuning issues due to the carbs orientation.

Aftermarket manifolds to mount a DCNF (or even a DCNVA / DCNVH variant) the "correct" way, so if you want to go the single carb route, find a manifold to suit, or modify the existing manifold by welding a new carb base to it in the correct orientation, it's not that hard to do, pre cut base plates are sold on ebay as "spacers" and a little mill time and skill with a TIG welder is all you need.
x19 sohc single dcnf 001.jpg


SteveC
 
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Thanks a lot for your comments and explainations !!
Actually the engine is in the workshop, I mounted new CPS Pistons with a diameter of 81 mm.
I have bought a new camshaft (from a 128 rally) and I'm waiting for a new handmade exhaust.
The valves have been modified.
The Flywheel (volano motore in italian) has been lightened (less 800 gr) and I hope that this jobs will give more power to my 128.
I will use it for some "regularity races" , I don't need more speed but the car must be faster in response and handling.
Many thanks to Steve, I have readed your topic and it's very interesting, I will consider it for the carburetor choice.

It's strange that the Fiat 128 it's an italian car but in Italy there are no forums and I have find this american forum with greate contents !!!

I will come back to you with some pics of the car...
 

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The 36 DCD is quite easy to found and it's cheaper compared to the 36 dcnf
If I have well understood will be the best solution (if I can find the manifold)
Correct ??
 

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it needs to be a 36/36DCD with simultaneous operation... not a 32/36DCD or another variant like that one there with a progressive throttle arrangement.. both throttle blades need to be the same size and open at the same time for best results.

36DCNF uses an enrichment fuel device for the "choke" ... a 36DCNVA uses a regular "strangler" flap to restrict the air and richen the mixture for "choke"... you can probably find a 36DCNVA cheaper again

36DCNVA 004.jpg


a 36/36 DCD would be a little more "period correct" for your historic type of regularity runs.

You can still buy manifolds new, Stole in Croatia casts a copy of the old Alquati, he can drill the flange pattern to suit either DCD or DCNF pattern, so a manifold is not that difficult to find.


SteveC
 
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It's strange that the Fiat 128 it's an italian car but in Italy there are no forums and I have find this american forum with greate contents !!!
While there are a lot of North American members, there are also a few European and Australasian members too, so I like think of this as a global community :)

Your car looks awesome from the pics you posted and sounds like you are doing some nice period mods. Would be good to see more pics, especially engine mods you are doing, if you have any,
 
While there are a lot of North American members, there are also a few European and Australasian members too, so I like think of this as a global community :)

Your car looks awesome from the pics you posted and sounds like you are doing some nice period mods. Would be good to see more pics, especially engine mods you are doing, if you have any,
I have the pics all of the works done on the car.
For each small particular I have done a complete restauration, I have changed or re-built and re-painted all..
Concerning the engine, now it's in the workshop to be restored and actually I have no pics.
,
 

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it needs to be a 36/36DCD with simultaneous operation... not a 32/36DCD or another variant like that one there with a progressive throttle arrangement.. both throttle blades need to be the same size and open at the same time for best results.

36DCNF uses an enrichment fuel device for the "choke" ... a 36DCNVA uses a regular "strangler" flap to restrict the air and richen the mixture for "choke"... you can probably find a 36DCNVA cheaper again

View attachment 81456

a 36/36 DCD would be a little more "period correct" for your historic type of regularity runs.

You can still buy manifolds new, Stole in Croatia casts a copy of the old Alquati, he can drill the flange pattern to suit either DCD or DCNF pattern, so a manifold is not that difficult to find.


SteveC
I checked the manifold on Stole racing shop..
Do you think that it's correct ??
 

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I checked the manifold on Stole racing shop..
Do you think that it's correct ??
that's for 2 x DCNF carbs... if you want a single carb you want this manifold


and ask him (from memory I think his name is Bojan) to drill it to suit a DCD base pattern if you go with that style of carb, and specify 128... as he also cuts the flange at the right angle for X19 (engine tilt is different for 128/uno/ritmo etc and X19)

It's a copy of the old Alquati, but without the water jacket.

SteveC
 
You will find a 36DCNVA a lot cheaper than a 36DCD7 or 36DCD3


they were used on some talbot / simca / matra (french) and also on some english fords

so ebay UK and ebay france are good places to look for used

SteveC
 
You will find a 36DCNVA a lot cheaper than a 36DCD7 or 36DCD3


they were used on some talbot / simca / matra (french) and also on some english fords

so ebay UK and ebay france are good places to look for used

SteveC
For DCNVA can I utilize the same manifold of DCNF ??

Do you have a list of the different meanings of DCNF DCNVA DCD etc..??

Thanks
 
For DCNVA can I utilize the same manifold of DCNF ??

Do you have a list of the different meanings of DCNF DCNVA DCD etc..??

Thanks
Yes, they are the same base flange bolt pattern / spacing.

The whole "family" of carbs, stemming originally from the DCN (which has a three bolt mounting pattern - just to be different) share the same bore spacing, roughly the same overall heights, and commonalities between internal parts. The family basically consists of DCNF, DCNFA, DCA, DCNVA, DCNVH, with loads of variants signified by a combination of numbers as a suffix after the main alphabetical nomenclature.

Unfortunately, Weber (like most Italian companies) isn't known for a rigid numbering system (not like the Germans for example) and the nomenclature darts around all over the place.

Only a few of the letters carry absolute meanings and position in the "name" of the carb type. D, for example, is supposed to stand for "Doppio Corpo"- Double Body (or two barrel) In the famous line of horizontal carbs, the DCO series the third letter position stands for "Orizzontale" - Horizontal.

The I in IDF and IDA, which are vertical two barrel (but also come as a three barrel) carburettors, is supposed to stand for 'Inclinato" - Inclined... but the I is in the first position and the D is second... so there is simply no definitive structure to the nomenclature of Weber carbs.

For the DCNF for example, some people have said the fourth F stands for Ferrari as the DCNF was found on the Dino, but the Dino V6 engine was just as much a Fiat effort in it's design and manufacture so the F could just as easily stand for Fiat. The second C is supposed to stand for "Corto - short" as the carburettor is known for it's low overall height, but it's a vertical carb and doesn't have the letter I anywhere in it's name....

SteveC
 
The Haynes Weber Carburettors Owners Workshop Manual has a pretty good appendix containing specific Weber model information by automobile manufacturer/model. For example, I've got a pair of 40 DCNF 47 carbs. This turns out to be one of the carbs used on the US version of the 308 GT4 (The other 3 being 45, 46, 48 varying by linkage for each location). The information for jets, emulsion tubes, etc. is also listed. I've also got a Weber book that has similar information but much less detailed.
 
Carburetor For Weber 38X38 2 Barrel Fiat Renault Ford VW Dodge Toyota Pickup Daewoo Lada Seat Opel Jeep BMW Mitsubishi 4 Cylinder DGEV Electric Choke Carb Replace OEM # 19830.202 DGES 390 https://a.co/d/au9VIaW

What about something like this? Is 38/38 too big? For a 1500?
 
What about something like this? Is 38/38 too big? For a 1500?
His car is 1100cc... that carb is made of chinesium :rolleyes:

DCD and DCNF/DCNVA have removeable chokes, so can be choked and jetted appropriately to suit any engine size, that carb has fixed chokes so lacks adjustment.

SteveC
 
How will that carb run on smaller throttle openings? More specifically, how will that carb behave overall versus a progressive carb like a 34DMTR? Also, is there any provision for a vacuum advance?
 
The DGEV you pointed to at least has simultaneous throttle opening, therefore twin minimum jets, and twin (central but two outlets) accelerator pump sprayers ... so it's a step in the right direction... it would still need to be mounted in a similar fashion to the DCD or DCNF/DCNVA ... i.e. it wont suit simply mounting in the same base orientation as the DMTR, as it , once again, is designed for float pivot / float bowl "forward" , not sideways...

A DCNVA is a good improvement in airflow capability over a DMTR... a DCA for example (very similar to a DCNVA/DCNVH) is used on the volumex models of Lancia/Fiat, and they are conservatively rated at 135hp, so it will easily flow enough air to that level of tune on any engine... a 34DMTR maxes out about 120/125hp.

The beauty of it for a single application IMO is the removeable chokes, and the idle mix screws / progression ports at the "rear" position of the carb which is simply the best overall position for even mixture distribution when fitted in the correct orientation using one of the manifolds described above, or modifying a standard manifold as I've shown... it's also a very simple throttle hook up as it maintains the same orientation as the stock DMTR linkage, off to the right hand side of the engine... the DCD and the DGEV would have the linkage to the rear, and need a bellcrank arrangement to rotate the throttle movement...

The 36 butterflies are a sensible step up from say twin 34's of the DMTR, and with twin 26 or 27mm chokes for a 1500 can get you over that 100hp at the rear wheels without too much fuss if the rest of the engine is built right... to get there with the standard carb orientation and a 34DMTR and 25/27 choke sizes is far more difficult and needs a lot more "finessing" to get there..

If you live in a climate where the choke isnt needed, you can simply lop the standard choke flap and the whole carb top off flat and install a regular DCNF bellmouth...

20210209_140958.jpg


20210209_140937.jpg


this particular carb is a DCA, as I wanted the power valve... It has AN type fittings added for fuel inlet and return, as the DCNVA only has a single pressed in brass inlet, which I removed, threaded the hole and added the AN fitting, the return I simply used a banjo bolt the right thread to screw into the usual large brass plug that holds the internal filter in place and added another tight radius 90 AN fitting for the fuel return.

it has a DCNVA modified top fitted to it, it to suit a regular 5 1/8 base K&N air box you can see in the background of this next picture where you can also see the original fuel inlet tail
20201014_205958.jpg



Yes the DCNVA has two vacuum points, one above and one below the throttle plates, so you could use either ported or manifold vacuum for ignition adavnce... the one below the throttle plates usually hooks up to the choke pull off capsule mounted on the side, but the hose is not fitted in this picture
36DCNVA 003.jpg


This is a short video of my linkage setup for this carb/bellmouth on an X19 racecar ... using a linkage rod from an automatic car that originally was for additional throttle movement to pull the auto kickdown cable... I've employed it to prevent stretching / snapping the throttle cable if there were too much force applied to the pedal... (which happens in racing) the linkage rod simply stretches in overall length and then returns to normal


SteveC
 
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