40 dcnf weber question

martijn

martijn

X addicted
Which camprofile of the accelaratorpump is most suitable for the x1/9. I have a nr 14 and i believe an 11. Which is more steep and aggressive but seems to rich. I hope for comments from other 40 dcnf weber users. Thx
 
Where is the ID mark on the cam? I just took a quick look on mine (mounted in car) but did not see anything. You might also check the pump jet. I'm using 0.45 mm on my pair.
 
I'll look at mine to see what it has. Everything on it is the way it came from the original Italian factory, except I changed the venturis for smaller ones.
 
I just checked mine and the marking is a circle with "11" inside. I have not driven this car since 1995, but between 1980 and then, the accelerator pumps seemed to be set up correctly. I bought these carbs new from Serra Enterprises so I'm guessing they came from the factory with those cams. The specific carb type is "40DCNF 47 7L".
 
I also looked at mine and it too has the #11 cam. As mentioned, that is how it came from Weber.
However I believe your question was what do we think of the effectiveness of the accelerator pump/cam we have. Unfortunately I can't help with that; for one thing mine is a single DCNF set up and I seem to recall you have duals so it's different, and second mine is still being built so I don't have much to report on how it works...sorry.
 
You change cam and pump jet, but there are also different pump covers and levers. Some have levers with two pump lever positions to choose from.
So it is hard to make a recommendation.
I would stick with the 11 and see how well it works.
 
I've also found there can be differences in the pump diaphragms, depending on the rebuild kit you get. Some have a slightly larger or smaller metal disc, or different shape "bulge" around the disc, or the length of the center pin can be a little longer/shorter. I don't know if these changes have much influence on the pump's output with Weber's, but other brands of carbs offer different pump diaphragms (with these differences) to tune the pump's output. So there might be some effect. For that matter, compare a newer soft pliable diaphragm vs an older firm rigid one, there's a big difference in how much fuel they pump.
Weber's have so many variables available for tuning that it can be difficult to determine which aspect to address.
 
I have dual 40 dcnf 12 and the pump jet has 82 or maybe 28 on the back. It measures 7.3mm at it widest.
15353247548781179604634824301332.jpg
 
Last edited:
For comparison, this is the big pump cam (number 11, I am using it with a 45 pump jet):
IMG_0127.JPG
I fact, it is so big that I had to grind the pump lever in two places so it doesn't bind with the linkage as seen in the pic.

Here are the two types of pump covers with one being adjustable:
IMG_0094.JPG
I read in an owners manual of some sort of Ferrari or Maserati that you are supposed to change the position of the lever pivot between summer and winter use!
Hilarious. I wonder how many times that was actually done.

My thinner cam is a number 42.
 
Last edited:
I don't have an 11 i see now, but something in between. the problem is that its way rich of trottle, because its quite steep of trottle already. i do have the pumps with the 2 holes. I had 2 sets of carbs and switches some parts out a few years ago, so i dont know which one came with the car. i have dcnf from an austin montego 100 en 101 i believe. will try to step down on idle jet first. going from 52 to 50.
 
IIRC, the 11 pump cam does not wirk with the cover with two holes. Too much travel, it bottoms out.
 
Ulix said:
I read in an owners manual of some sort of Ferrari or Maserati that you are supposed to change the position of the lever pivot between summer and winter use!
Hilarious. I wonder how many times that was actually done.
Click to expand...
But so typical of how they designed things back then. Like you say, how often did it ever get done.
 
I was having a very lean idle but above 3000rpm it was perfect. Changed to a 65 idle jet and thing are much better. No stumble off idle.
200 ac
F24
130 main
32 choke
4.5 aux Venturi
I don’t know what the pump jet size is.
 
hi. i spend mutch time with that. all 40 and 42 44 have problem at 2000-2800rpm. only 36 dont hve that. i spend many times and i see at internet tell 1 site all have problem dcnf 40 42 44. the same. i have idf 40 now and i have 3hp more and 0,6nm up. 1,5 year now. perfect.
 
You must log in or register to reply here.
Back
Top