twin weber DCNF(VH) throttle linkage ideas needed...

M

Marty Decker

Low Mileage
Hey Folks, I sure would appreciate ideas and photos on creating a throttle linkage for the new twin Weber carbs I am installing on my X/19. I have a PBS manifold. The throttle rotation on the twin carbs is opposite of the stock carb. One suggestion I was given was to turn the carbs around on the manifold so the float bowl is to the front of the car and the air mixture screws are facing the back of the car. Thus reversing the direction of rotation. Other suggestions have been to go in with a customized cable looping around the carbs and affixed to a bracket fabricated to mount where the carbs bolt to the manifold. Some photos I've seen look like maybe the throttle crank of the inter-carb linkage has been inverted so as to change the direction of rotation and was then driven by a rod coming off the exiting throttle shaft attached to the cam housing cover. Hoping that knowledgable people will help me out with this.
Thanks
Marty in Alaska
 
float bowl forwards and mixture screws to the back is the "correct" mounting for a DCNF/DCNVH/DCNVA style carb.
20180122_130505.jpg



SteveC
 
"so the float bowl is to the front of the car and the air mixture screws are facing the back of the car." - This is how they should be mounted.
upload_2019-2-19_20-59-26.png
 
Sure do appreciate you responding Steve! Sooo, the Weber distributor that I purchased the manifold and carbs from mounted them backwards, huh? Nice. Good people, but they don't know Fiat. Well, I have a feeling that life just got a little easier...I'll swap them around. That's a sweet, "done right" set up you have there. Could I trouble you to give me other angles and images of your throttle linkage? I can't quite tell what you've done up on the cam housing cover, nor at the carb end.
Thank you!
Marty
 
This is how my DCNFs are mounted:

1974 Fiat X19 Dual 40 DCNF.jpg


The linkage is connected to an after market arm on the stock 1974 cam cover mounted throttle shaft.
 
You too Brad, thank you! The cable idea gives me another option it's pretty clear in your photo how you did that. I appreciate you guys setting me straight on how the carbs should be mounted on the manifold...
 
Thanks "dllubin", you guys have been totally helpful! Would appreciate any additional photos people have of their solutions to fabricating the linkage.
 
Marty Decker said:
Thanks "dllubin", you guys have been totally helpful! Would appreciate any additional photos people have of their solutions to fabricating the linkage.
Click to expand...
Marty:

Here are a few closeup photos:

1974 Fiat X19 Dual 40 DCNF Linkage Closeup - Cambox.jpg


1974 Fiat X19 Dual 40 DCNF Linkage Closeup - Carb.jpg


1974 Fiat X19 Dual 40 DCNF Linkage Closeup -Top View.jpg


Note that the threaded throttle rod has about a 30 degree bend in it where it is passing under the fuel inlet for clearance.

Don
 
There are many ways to link up to the DCNFs, it's very cheap and easy to use the stock linkage. You start by turning around the lever at the end of the linkage (circled), then bending the connecting link as seen in the pic below. (I swiped this pic, if this is your car please chime in.)
InkedGEDC0003_LI.jpg

If you really want to do it simply you can avoid the bend. (Not that I recommend it, but, it can be done.) (Another swiped pic!)
s-l1600.jpg
 
Marty's post of reverse linkage is strange, I have never seen DCNFs on an X with reverse rotation to the stock carb (or FI). Was there a version of DCNFs that had reverse rotation? I know the DCOEs were a pain on my X because they did have reverse rotation.
 
Thank you Mike and Carl for taking the time to answer. Mike, that is an awesome solution! I'm on it! Carl, I learned from others that the carbs were mounted BACKWARDS on the manifold when I purchased them from a Weber shop which had acquired PBS manifolds (when they quite doing Fiats) which explains the counter rotation issue. Crazy, huh? I sure do appreciate your help.
 
Steve, that is an absolutely BOMBER solution. Someone with the mind of a true engineer came up with that brilliant execution. Please thank Mark for taking the photos for me. And I truly appreciate you providing such bonafide info and assistance...from half way around the world!
 
Thanks.

The trick with linkages it to have the lever arms "clocked" correctly to give a smooth operation. Weber recommends 37 degrees off vertical tilt for the throttle levers.. most throttle plates are 78 or 82 degree plates... so having the lever tilted more or less half the throttle plate angle will put the lever approx the same angle on the other side of operation at full throttle.

The other is to keep the relative lever lengths the same, to get a smooth EVEN operation throughout the full range.

I look at the pics and the first thing I notice is "I forgot to trim the threaded rod on the ball"

The carb balance interlink started life as a weber part for DCOE carbs... as this is about all you can get for the interlink parts these days...from there I modified it to suit the DCNF's. The adjustment link is easiest to adjust if you set it up with the balance screw vertical for easy access.

The cam box lever arm, the ball fitting, the carby linkage rod are all off the shelf aftermarket items from "Redline"

Fitting bellmouths as shown in pics was worth 8hp at the back wheels (109 hp at the treads on this motor currently)

SteveC
 
Last edited:
fiatfactory said:
float bowl forwards and mixture screws to the back is the "correct" mounting for a DCNF/DCNVH/DCNVA style carb.
View attachment 19682


SteveC
Click to expand...
Ah ha! Looking back through my posts from four years ago, I see where you were the guy to set me straight on how Pierce should have mounted the carbs. When I informed the owner, he was blown away that after selling many such set ups over the years, NO ONE had contacted him to let him know he was bolting them up improperly! Hope you can help me on the DCNVH issue...obviously I have been distracted from this project, but, by golly I'm back ON it now. Yeah, turns out the carbs were not DCNF's. Your set up (above photo) is DONE RIGHT!
 
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