For grins I removed the Supersprint filters and air horns tonight. The stumble is 100% cured. Has anyone experienced this before??? Seems odd that an air filter can cause the car to stumble so badly. Am I missing something?
Guess I'm in the market for a Euro OEM airbox setup for an Alfetta now. Anyone have any leads where I can source this?
You may have created a "pulse plate" by having the air horns too close to a solid surface, i.e., the hood in this case. Max Banks has an interesting post on this in the "Aluminum Inlet Manifold Extender. . ." thread.
Jim,You may have created a "pulse plate" by having the air horns too close to a solid surface, i.e., the hood in this case. Max Banks has an interesting post on this in the "Aluminum Inlet Manifold Extender. . ." thread.
That's certainly possible, particularly with straight air horns inside a filter air box. In this case, 1150ss' curved velocity stacks make this a bit less likely, but clearly there's some restriction inside the filter box. It sounds like the best answer, based on the previous owner's experience, is to run the velocity stacks with filter socks.
But 1150ss' comment "The stumble got a bit better after adjusting the idle screws" leads me to believe that the carbs aren't properly synch'd. The idle mixture screws on DCOEs are easy to mess up by blind trial and error (and dead simple to get right with a synchrometer). And I'm still willing to bet that those idle jets are too rich.
On a 1.6L, I'm running DCOEs with exactly the same jets & tubes as 1150ss, and curved velocity stacks (although without the filter box), and I had the same issues. The stumbling was instantly cured by synch'ing the carbs, and the light throttle running was further improved by dropping from 50F9 to 45F9 idle jets (although 50F8s may also work).
You are so right about this. With my first Alfa, a 1600GTV, I'd watched experts tune the Webers by ear. It didn't seem that difficult, so I decided I could do it myself. I drove around ----for months---with a very long skinny screwdriver and tweaked the Webers everywhere I went until I finally learned how to get the car to run right. It's really easy to create the kind of stumble we're talking about. I had it for months.The idle mixture screws on DCOEs are easy to mess up by blind trial and error (and dead simple to get right with a synchrometer). And I'm still willing to bet that those idle jets are too rich.
While you can learn to tune Webers by ear, a tool like a Synchrometer makes the job much easier and more accurate.
Couldn't possibly agree more. In addition to the Passini, the Weber Technical Manual (occasionally available on eBay) has a good--if translated from the Italian--discussion of carb operation, as well all listings of all jets & correctors and technical drawings with the dimensions and drillings for every emulsion tube.IMHO every Weber owner should have two tools: a Synchrometer and a Colortune.
Oh, yeah. The Passini book has a good discussion of how the transition from the idle circuit to the main circuit is influenced by jets and emulsion tube choice. I think a true measure of being an Italian car enthusiast is being able to read, and understand, the Passini Weber book. Enlightment does come, but only after much pain. I think Passini just dictated his ideas into a tape recorder, transcribed, and then published 'em. There's not much evidence of editing, but the ideas are actually pretty good.
Well, that’s an excellent point; I’m running much older DCOE 15s; I certainly can’t vouch for the jetting and emulsion tubes of the later emission-series carbs.I think that you have the completely wrong idle jets and emulsion tubes. 40DCOE149's are emissions type carbs. The idle circuit is fed from the well and not the float chamber, as on "classic" carbs. They require different emulsion tubes and idle jets. I posted a list of suitable idle jets in rich to lean order a year or so ago. I am at work and I don't have the data in front of me but I think that you need F34 emulsion tubes and 55F17 idle jets.
Thanks for all the advise guys!
The carbs are properly synchronized using a Synchrometer. Tried both 50F8 and 45F9 idle jets and the stumbling was MUCH worse. Can't get my hands on 55F17 idle jets to try.
At this point I am wondering if I should go back to the velocity stacks and socks ???
Cheers!
Scott
I would think you might want/need more fuel in which case going to a 55F11 might be correct as that is the next size relating to fuel flow.I size richer is 50F9. One size leaner is 50F11
I´m very much missing pump jet and pump back bleed valve size used in your application.....130mains are standard in DCOE32´s for a 1750, so may be to small for a slightly hotter 2l.....just my thoughts.axis_powers said:32 chokes
130 mains
currently running 50 f9's(have 50f8's)
195 bleed
F9 emulsion
