Single Weber DCNF

H

halojm

True Classic
I picked up an Alquati single DCNF manifold and both a 40 DCNF carb and a 36 DCNF carb. Any ideas what jetting and what kinds of adjustments to use as a base line for these carbs with my 1500? ('80 1500, block decked .040", ported/polished Euro cylinder head shaved .060", Euro cam advanced 2 degrees, ported Euro 1500 4-2 exhaust manifold with 2 1/4 exhaust, lightened flywheel, lightweight crank pulley)
Thanks, Dave
AlquatiDCNFManifold.jpg
 
Perfect

Just what I was looking for. It looks like either the 36 DCNF or the 40 DCNF will work, so I'll just have to figure out which one is better on the dyno.
Thanks, Dave
 
Keep in mind that those are dual carb installations....

Just reminding.

Look up the stock jetting for a 34 DMTR and that will get you close. Just depends.....on a lot of things. What size are the venturies in the 36 and the 40?

Weber has a series of formulas and charts to determine jetting (that I don't remember any more because it has been like forever since I tuned a carb) that take you through in sequence, venturi size, then main jet size, and then air correctors, then idles. You will be running a bit different animal than the above mentioned 34 DMTR, but running the same sort of jetting will get you somewhere in the ballpark.

It is great that you are going to dyno tune. Get lots of jets. I might still have some mains, A/Cs and idles around, tho' no sure thing that I have two of any given size. Lemme know.

Ciao,
 
My other X

(with Dick in LA, that I got from Warren in Canada) has a 40DCNF on it. I remember the grins I gave myself driving that car. Took it over to Mark Freemans house one day and let him take it for a spin and he came back with eyes as wide as saucers. The thing hauled butt. Of course, besides the 40DCNF, it had a 35/75 Faza cam, Ansa exhaust, and coilovers, but man, that 40DCNF was sweet.
 
I am about to put that same set-up on my ugly brown X...

...with a 1300 head, 35/75 cam, PBS header and Dynomax muffler.

BB 4RE also has that set up and is jetted correctly. Perhaps the people that just bought her from Bob Brown could pull the jets and give you the numbers. I cannot recall what they were anymore. Mine won't be installed for a couple of weeks.

It is definitely a hot set up. I have had 7 X's and the single DCNF has been my favorite to date.
 
+1

I dimly remember discussion on single DCNF jetting (maybe back when Steve Soar had his race car with the single carb?) how different the jetting was compared to a dual setup.
Makes sense, on a dual install, one cylinder acts on one venturi, with the single install, alll 4 cylinders act on each venturi.

I also seem to remember that my impression was that it is hard to set the single DCNF up to run well, but from comments in this thread, this may not be so.
 
Check to see the manifold is actually for an X19, as Alquati never made one specific for the X, they only made them to suit the engine tilt of the 128.

Sprint made one to suit the x19, so perhaps it's one of those?

The problem with the dcnf manifold, is that originally the setup was designed to use a 36DCD. Now on a DCD the throttle blades are not on a single shaft like the DCNF. The DCD has two shafts and the butterflys tip towards each other... the DCNF having a single shaft the throttle butterflys tip forwards.

With the DCNF this creates a mixture distribution problem at partial throttle, the centre two cylinders being richer than the outside two. Not a big problem at WOT as the individual mixtures tend to sort themselves out. Running a carb spacer works well on these manifolds, and can be helpful in evening up part throttle mixture distribution.

SteveC
 
Never had any issues with this set up...

...from what I recall it was just a trial/error method on the jetting, much like any other jetting situation.
No throttle response or mixture problems, either. Never had a manual choke run for it, so I had to nurse it a bit until warmed up; but once warmed up it never skipped a beat.
 
I checked the angle of carb mounting

and it is the same as a spare X manifold I had laying around. I've got a few carb spacers I was going to play with to tweak it for HP and torque.
Dave
 
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