Dual Weber 40 DCNF setup

[Fiatz124]

My 1800 spider ran well with the stock carb, but I recently acquired a Bayless dual carb kit along with some other goodies at a good price. So I installed Alquati 40/80 cams, an alquati dcnf manifold and dual weber 40 dcnf carbs. The engine starts and runs under idle, but will not accelerate at all. It pops and stalls out under any throttle. The jets may be "off" from what Bayless recommends, but the venturis are also smaller so they could be accurate. The box of parts also includes a facet sold state fuel pump. Open to suggestions. . .

Here's a vid of the engine at idle - https://youtu.be/B4d7hdPBwqo

[grrrdot]

I've never worked on DCNFs but assuming they are similar to IDFs it sounds like something with the transition circuit or accelerator pump.
I would check the idle jets, idle passages, Idle stop screw position, Idle mixture screw and look real close for vacuum leaks.
My IDFs were leaking like crazy around the throttle shafts which created all sorts of issues.

-G

[Nut124]

I run the same setup in my 1800 and it runs fine except for the lean rt turn.

I would have to check my notes to verify jetting.

I seem to recall that I had to modify the accelerator ramps, they were too steep.

Does the engine run on the road under load at constant speed at all?

Got a header?

[Fiatz124]

Hey guys thanks for the input, finally got it going today. I borrowed a timing light and checked the timing. . . was retarded by at least 30 degrees. Re-timed to 5* advance and now idles and revs just fine.

[Fiatz124]

I run the same setup in my 1800 and it runs fine except for the lean rt turn.

I would have to check my notes to verify jetting.

I seem to recall that I had to modify the accelerator ramps, they were too steep.

Does the engine run on the road under load at constant speed at all?

Got a header?

As for jet sizes, I currently have:

30mm chokes,
.12mm main jets,
.06mm idle jets,
F25 emulsion tubes

How did you setup your throttle linkage?

[Nut124]

I run 34's and 125 or 130 mains.

The carb linkage I fabricated myself some 20 years ago and it has not needed adjustment since. I tried to take some pictures but it is hard to get there w/o removing the air cleaners.

[Fiatz124]

Thanks for the pictures, I can't really make out exactly what it looks like. . . but I get the idea. Looks like you have the cable pulling a lever, and on the other side you've got something pulling the throttle back (in opposite direction of cable movement).

I tried a proof of concept today to see if the original linkage could possibly work.





Looks like even if I mechanically locked them, the throttle rod would get caught on stuff, and not have enough travel

[Fiatz124]

So I found a little throttle tab with a ball on it from another carb I had laying around. Secured with a nut on the throttle shaft, I was able to connect the stock throttle cable and fasten it to the brake master cylinder using zip-ties. This is temporary of course, and dangerous so I wouldn't recommend to anyone, but I did this to demonstrate how it worked as well as throttle cable position. I'm considering making a bracket that comes off the two inner corners of the carbs and holds the cable in place above the master cylinder (without touching the master cylinder).

My issue now is that the idle mixture screw furthest to the right is only millimeters away from the brake booster, and contacts it in reverse. One way I can think to correct this, is to remove the carbs and orient them 180*.

@Nut124, did you have this issue?

[Fiatz124]

So. . . got to tinkering again and think I cracked this puppy. Firstly, I decided to switch the carbs back around to avoid contact to the brake booster. While I was at that, I figured maybe I can use the original throttle linkage.

Then, I found a little throttle tab on ebay that could be fastened to the carb throttle shaft. This allowed me to use the original throttle linkage assembly, all that was left was to bend the throttle pullrod to avoid contact with the valve cover. <-- hope I'm speaking english

Here's some pics VVV





I took the little fiat for a spin, and man does it pull!!! The sound is remarkable, almost racecar-ish. Totally worth the effort. Although the carbs still need some tuning to get it running just right, and the engine bay could use some tidying.

Hope this info helps someone !

[Fiatz124]

Here's a couple low quality videos of me revving the piss after the conversion.

https://www.youtube.com/watch?v=q7n1CaA861o

https://www.youtube.com/watch?v=dgrYMO5MkAM

Enjoy !

[Nut124]

Here's a couple low quality videos of me revving the piss after the conversion.

https://www.youtube.com/watch?v=q7n1CaA861o

https://www.youtube.com/watch?v=dgrYMO5MkAM

Enjoy !

Glad you are making progress. That orientation is going to make it very difficult to adjust the carbs. I find myself adjusting the idle jets and idle speed somewhat frequently.

In my pictures above, the carb cable bracket is attached to the flat on the header, where the Alquati text is. The pull reversal system is attached to a cam box bolt head. Both brackets were fabbed from stainless flat stock with the pivot point welded.

The carb linkage sees a lot of stress and needs to be properly set up or something will break and leave you stranded.

[Fiatz124]

@Nut124 , adjusting the carbs in this orientation is actually not so difficult with the right tools. The benefit of this setup is being able to use the original throttle linkage and return springs, which I think will be reliable for many years to come. Also, the rear carb is no longer contacting the brake booster under load. Overall I've been very happy with it !