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PostPosted: April 21, 2018, 12:36 pm 
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Joined: November 11, 2013, 4:47 am
Posts: 796
Location: No. Nevada
Similar displacement Alfa Romeo 1600 factory sets for comparison.
Your bore and stroke probably differ so what works for Alfa may not be correct for you but I would expect some similarity.

Giulia 1600 SS
Engine capacity: 1570 cc
Weber model: 40 DCOE 2
Choke: 30
Auxiliary venturi: 4.5
Main jet: 120
Idle jet: 55F11
Emulsion tube: F16
Air corrector jet: 180
Accelerator pump jet: 35
Accelerator pump back bleed: 70
Needle valve: 150

Giulia 1600 Sprint GTA
Engine capacity: 1570 cc
Weber model: 45 DCOE 18
Choke: 30
Auxiliary venturi: 4.5
Main jet: 120
Idle jet: 50F8
Emulsion tube: F9
Air corrector jet: 220
Accelerator pump jet: 35
Accelerator pump back bleed: 50
Needle valve: 150

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PostPosted: April 30, 2018, 6:44 pm 
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Joined: February 15, 2018, 8:32 pm
Posts: 38
Location: Vancouver, BC. Canada
Time for an update.

I’ve collected a good assortment of Weber jets that allow me to swap and test different AFR configurations.

My first goal was to get the engine to idle smoothly with an AFR around 14:1. Currently with the 45F9 idle jets, the best idle I can achieve is 13.5:1. Any further adjustment of the idle-mixture screw would upset the idle.

So I replaced the 45F9 idle jets with 40F9’s. Now I can get it to idle nicely at 1000RPM with a measured AFR of 14:1….however any blip of the throttle would send the engine way lean (pegged the AFR gauge).

So, it looks like any change to the idle mixture circuit, impacts the main fuel mixture as well.

I guess the next step is to installed large main jets to compensate for the leaner idle jet.

I see tuning Webers is an iterative process....stay tuned.


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PostPosted: April 30, 2018, 8:30 pm 
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Joined: May 27, 2006, 9:46 pm
Posts: 1820
Location: BC, Canada. eh?
The "falling on its face off idle" syndrome is a common one. It's exacerbated in engines such as the Ford Zetec which, due to their valve train design, take in a LOT of air, VERY quickly. The 45DCOE's were not particularly well designed for this, and the problem is one of a lack of fuel available just off idle (i.e., in the instant when the butterflies first open a tiny bit). There's a big slug of air, and not enough fuel to provide a proper stoichometric mix.

Weber, in concert with Webcon in England, has recently designed carbs that (reportedly, at least) completely cure this. They do this by adding a series of extremely precisely sized & located "progression holes" around the lower edge of the butterflies. These holes connect directly to the fuel supply, so instantly enrich the mixture at that critical point.

There are other Weber 45DCOE's that work reasonably well, too (although, not with the Zetec), having 3 or 4 progression holes. Older design engines often benefit from these carbs. The Alfa Romeo forums abound with information about this problem, and solutions sought. It might be worth browsing some of those sites for further ideas.

As I'm using a Zetec, with a very short, VERY non-restrictive manifold (I can clearly see all my intake valves through the carbs when I crack open the butterflies), the brand new design 45DCOE's were my only choice to get the engine running right, so I just recently bought a set & had them shipped over from the UK. They're specifically designed for my engine, in its current state of tune, so they should be jetted very close already.

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PostPosted: May 1, 2018, 2:45 pm 
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Joined: February 15, 2018, 8:32 pm
Posts: 38
Location: Vancouver, BC. Canada
I now understand why the PO had the idle set north of 1200RPM. Bad for fuel consumption, but it minimizes the off-idle stumble.

If I lend up keeping the car, I'll probably go EFI. There are some nice systems out there and the prices seem to have stabilized.

In the interim, I'll keep fiddling with the Webers.


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PostPosted: May 1, 2018, 3:55 pm 
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Joined: May 27, 2006, 9:46 pm
Posts: 1820
Location: BC, Canada. eh?
As far as Zetecs are concerned, in the UK the "solution" (if using the older style Webers) was to run them blubbering-rich at idle, in hopes that in transition (as the butterflies start to open) there's enough richness left over to get past the stumble. Not surprisingly, though, once the cars were off the idle circuit they carbureted perfectly...because the "high speed" circuit is independent of the "idle" circuit.

Trog - another possibility for you might be to find a pair of Webers with third, or even fourth, progression holes. They're definitely out there, once you know what you're looking for, as they've been used on some European makes (like Alfa) for years. A search for Weber 45DCOE 152-G will reveal the later, 4-hole variants. It's amazing how many different models of 45DCOE 152 series carbs exist.

The 5 progression hole carbs I bought were designed specifically, and solely, for the 2.0 liter "blacktop" Zetec. Nonetheless, a lot of Alfaholics are looking at them hungrily...

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Scratch building, at continental-drift speed, a custom McSoreley-design framed, dual-Weber 45DCOE carburated, Zetec-engined, ridiculously fast money pit.

http://zetec7.webs.com/


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PostPosted: May 1, 2018, 5:14 pm 
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Joined: December 29, 2007, 10:41 pm
Posts: 855
Location: Vancouver, BC
Trog,
I would recommend joining the Sidedraft Central group on the Yahoo boards. Keith Franck seems to be very knowledgeable on all things Weber. He makes different style jets and I think he has jigs for re-drilling the progression circuits. His parts aren't dirt cheap, but from the feedback he's getting, they do seem to work.

Rod


Last edited by cs3tcr on May 2, 2018, 11:57 am, edited 1 time in total.

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PostPosted: May 2, 2018, 11:18 am 
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Joined: February 15, 2018, 8:32 pm
Posts: 38
Location: Vancouver, BC. Canada
cs3tcr wrote:
Trog,
I would recommend joining the Sidedraft Central group on the Yahoo boards. Keith Franck seems to be very knowledgeable on all things Weber. He makes different style jets and I think he has jigs for re-drilling the progression circuits. His parts are dirt cheap, but from the feedback he's getting, they do seem to work.

Rod


OMG....just strarted into the Sidedraft Central Yahoo group....what have I got myself into? So overwhelming.


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PostPosted: May 3, 2018, 1:13 pm 
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Joined: February 15, 2018, 8:32 pm
Posts: 38
Location: Vancouver, BC. Canada
"eureka" with a small "e".

Out of desperation, I've been swapping out jets in the hopes of improving drivability. I've finally come up with a configuration that dramatically improves the driving experience.

With original Idle Jets (45F9) and an idle set to 1100RPM, I was able to tune in an idle AFR of 13:1. With this arrangment, the off idle stumble is gone and the engine idles smoothly!

The better news is that I've dropped the main jets from 1.15 to 1.00 which resulted in absolutely no transition stumble at all. AFR on WOT is 12.5:1......right on target!

Only one issue remains:

-A little pop out the carb on the overrun. I'm hoping this is a timing issue? Perhaps not enough advance? (I hope it's not a burnt valve).

Stay tuned....

T


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PostPosted: May 7, 2018, 6:09 pm 
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Joined: August 8, 2014, 6:08 pm
Posts: 631
Location: Green Bay, WI
The last time I talked to Dennis Brunton he said he raced with 12psi. I have 12 in mine right now and have been driving the car like this. its fine. I don't even make a bump in the sidewall. I don't know if I would be able to tell if one is flat. :shock:

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