Tuning 36dcnvh carbs for x1/9

Balgowlahx1/9

Low Mileage
I installed a pair of double downdraft 36 DCNVH carbs today, having bought them new with manifold years ago. I've only had some mild head work, lightened flywheel, and 4/2/1 exhaust fitted to my 1300 and found these carbs gave a lot more power but with throttle control difficulty at low revs. I have 28mm chokes, F36 emulsion tubes with 115 main and 170 air correction jets.
It's not bad at low revs when cold, getting worse with increased temp, so I'm thinking the jets need changing.
These are very basic carbs with all the choke stuff removed and I'd love to get them smooth at all revs.
Any ideas would be great please.
Andy.
PS. I'd forgotten the fabulous multi Weber induction noise.
 
Carb Jetting

Contact Pierce Manifold in Gilroy, California. That is where they probably originated from (your carbs and manifold). They have a data base on jetting recommendations if you give them your engine modifications. They can provide you with the jets as necessary.:)
 
Andy... Do you still have the original carb?

If so... or if not... imagine the amount of fuel you are dumping into that little engine no... as compared to the PROGRESSIVE operation of the one 32 and now the DIRECT operation of your TWO 36's...

No wonder to me why a choke is unnecessary when cold... and its also no surprise its running too rich when warm.

This set up is really made for all ON or OFF racing... and not for tootling around the neighborhood.

With tons of hours playing around with this stuff, you will eventually get it to run PERFECT for that DAY if lucky... Temps, Humidity and Altitude will impact the drive-ability as well...

Have fun... yur gonna love tinkering with this! If not, then go back to a progressive single carb.

As you said though... there is nothing like the sound of all four throats running wide open though. Ya gotta pay for it...

HTH
 
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:bla::bla::bla::bla::bla:

Gotta completely disagree with nearly everything you just said. Dual-DCNF (& dual-DCOE) carb setups have been successfully run on street-driven X1/9's & 128's for almost FOUR DECADES now. Provided that they are paired with the other suitable engine improvements (head/valve work, h/c pistons, better exhaust, etc.), once the jetting issues get dialed-in, this setup is quite reliable on NON-TRACK driven cars as well as on-track ones. Naturally, fuel mileage will go down a bit vs. a stock single-carb setup, but performance will go UP - which is exactly why folks install the dual-carb setup.

The sky is NOT falling... :)
 
Paging "fiatfactory"...

Contact Steve Cecchele (aka "fiatfactory") here on Xweb, as he sells this conversion kit from time to time & would likely have the correct jetting specs for these carbs in this particular application. Specs should be very similar to a dual-DCNF setup, since the DCNVA is from the same carb "family". :wink2:
 
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DCNVH

Contact Pierce Manifold in Gilroy, California. That is where they probably originated from (your carbs and manifold). They have a data base on jetting recommendations if you give them your engine modifications. They can provide you with the jets as necessary.:)

The DCNVH carb was originally used on the Maserati BiTurbo (in a single-carb application). They are often used on the dual-DCNF manifold as a cheaper (more-affordable) alternative to the DCNF. Pierce used to get their manifolds from PBS, not sure what they do now. Being a Weber supplier & DCNF's being a common performance carb, Pierce can usually provide most of the needed parts for either carb since they're related.

A very good "junkyard score" if you come across them! :grin:



 
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Agree!

I even had the 42's on mine. it was a daily driver in Michigan, through winters, and the only hiccup I had ended up being an exhaust issue. still got ~28 MPG as well. (for the daily driving, not the full out weekends)


Odie
 
Thanks all for your (mostly) positive postings.
While waiting for Steve's reply to my email on jet sizes I thought I'd look at the float levels as the main jets were awash with fuel. Without being able to find the levels on the internet I tried lowering the fuel cut off level by 4mm and the car drives much better although still not liking full throttle at low revs.
Cheers,
Andy from a very cold Sydney.
 
DCNVH has about five different settings for float height, you need to provide the suffix at the end of the carb nomenclature for me to be able to advise on float height, and even then I may not have the correct Weber template for that particular carb, the Weber bible I have only lists Italian vehicles, and the DCNVH 's you have are probably of something like a leyland Maestro or something French (even worse!)

Jetting looks about right, but you haven't advised what idle jet size you have, and I would be trying a set of F24 emulsion tubes ... as that is the standard go to E tube for twin carbs on sohc, trouble is that E tubes are expensive (unlike basic jets which are quite cheap)

Edit: did a quick google, came up with this on the fitment description of a carby overhaul kit at Webcon in the UK
Original Weber service kit kit for DCNVH 36 carburettor as fitted to:-

Sunbeam – Alpine 1.6&Horizon 1.6
1501 1.3 GLS ( 1294cc) & 1.5 GLS (1442cc)
1307 GLS ( 1294cc) 1308 GT ( 1442cc)
Hillman Avenger 1.6
Talbot – Matra Murena 1.6 &Solara 1.6

SteveC
 
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Thanks Steve. I bought the carbs on a "128" stamped manifold from NZ years ago and just now used a mirror to check the numbers on the outside of the float chamber. Both carbs show 'DCNVH 5/101 DA' . Hopefully that number plus my idle jet size of 42 helps.
The 1300 engine has had the head shaved and "ported", a lightened flywheel and the 4/2/1 exhaust. The 'new' carbs have made an amazing difference in performance, so it's only the 'take off from stopping' driveabilty that needs sorting out.
Cheers,
Andy.
 
No specs for those, but a quick web search found what they were made for...

http://www.automobile-catalog.com/car/1981/1458770/talbot_matra_rancho_decouvrable.html

and it's french... :shock:

if your manifold is 128, then chances are the carbs are tilted, which is why the floats were too high...and adjusting them helped

42 is a bit small on the idle, 45 to 55 would be the usual range (ie 50 +-5), too small an idle jet will sometimes cause a hesitation off idle...

Post a vid of it at idle, (8/900) lift the revs by 500 and hold for a few seconds, and again...if it idles OK, but 'fluffs' when held steady at around 1500, then usually the balance isn't quite right...one carb could be ahead of the other and this certainly causes a moving off from rest stumble...

SteveC
 
manifold

there is an 18 degree difference between the 128 and x, since the motor in the 128 is more "stand up" as opposed the cant of the x.
you might have it shaved to the x profile before digging into the carbs to take that out of the equation.
mikemo
 
I installed a pair of double downdraft 36 DCNVH carbs today, having bought them new with manifold years ago. I've only had some mild head work, lightened flywheel, and 4/2/1 exhaust fitted to my 1300 and found these carbs gave a lot more power but with throttle control difficulty at low revs. I have 28mm chokes, F36 emulsion tubes with 115 main and 170 air correction jets.
It's not bad at low revs when cold, getting worse with increased temp, so I'm thinking the jets need changing.
These are very basic carbs with all the choke stuff removed and I'd love to get them smooth at all revs.
Any ideas would be great please.
Andy.
PS. I'd forgotten the fabulous multi Weber induction noise.
I'm wondering how the DCNVH's worked out on your X/19. I too have a pair of them and manifold purchased from Pierce Manifolds some years ago. Just now getting around to installing them. I've learned that they were not meant for a dual carb set up and that they lack the air correction screws that the DCNF's has and which permit a person to balance the carbs. Was this an issue for you or are the DCNVH's working well on your X? I'd appreciate any information you have on how well the DCNVH's are working as a dual carb set up on an X/19.
 
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