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post #1 of 61 (permalink) Old 09-15-2014, 02:54 PM Thread Starter
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Fuelling issue Weber DCOE

I have a fuelling problem with my 1600 GT Junior running 40DCOE 44/45s, and I assume it's the idle circuit on the carburettors.

The mixture screws need to be turned 6 turns for the car to idle correctly, and the #1 idle screw had no effect at all! I've also balanced the carbs but #1 is drawing slightly less air than #2..ie the same carb is out of balance.

It's been sat around for over a year with little use and I assume this probably hasn't helped. It idles ok now but the pick up from idle to about 2000-2500 is awful, sounds like it's running on 3 cylinders almost, after that no problem.
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post #2 of 61 (permalink) Old 09-15-2014, 03:10 PM
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Looks like air leaks past the throttle. Do you have the OVS inlet on your manifold (small nipple on #1)?


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post #3 of 61 (permalink) Old 09-15-2014, 11:25 PM Thread Starter
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I think my manifold is different to the one you have QV.
Should this thread really be in the'Technical'section?
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post #4 of 61 (permalink) Old 09-16-2014, 09:18 AM Thread Starter
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How do I get this moved to Technical/Carburetors, Fuel injection etc.?
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post #5 of 61 (permalink) Old 09-16-2014, 10:14 AM
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I moved the thread.
The need to be turned out 6 turns to get it to idle? That would be an indication of at least too-lean idle jets if you're having to open the screws that much.

An idle screw that has no effect can mean a few things. So it runs OK on all four once it clears its throat? Have you checked compression and done and ignition check/tuneup first?

What engine, what carb specs? Maybe we can compared to stock Alfa settings and see if you're even in the ballpark.

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post #6 of 61 (permalink) Old 09-16-2014, 02:21 PM Thread Starter
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Thanks Andrew.

The engine is a 1600, original to the car as far as I know, so year 1975. It has twin Weber 40DCOEs, one is a 44 the other a 45. It has 30mm chokes. I did a compression test at the weekend and that was fine, all 200 psi. And it does run fine when opened up beyond the progression holes.
The carb mounts are rubber and they were replaced a few years ago, there's some slight perishing but nothing major.

I checked the throttle valve as it passes the progression holes and there's a tiny tiny difference between #1 and #2. Could that be causing the difference in suction between the two at idle and in turn cause the rocking of the engine?

The idle jets that it came with it are 50 F15 which are seriously rich I think. So it all points to the previous owner realising the problem and using extra rich jets. I tried 45F9s and I had to undo the screws until they almost came out.

I bought a service kit for the carbs today and had my first go at opening them up. Jets all seemed clean but I cleaned them anyway. And I had a look at the progression holes and ran some air through them and back up to the float chamber. Unfortunately the mixture screws that came in the kit are for the newer type DCOEs, ie they have a constant taper to the end. Mine have a step in the taper, but they looked in good condition so I'm not too worried about that.

The only thing that was slightly amiss was the float levels. According to the manual I have, the GT Junior 1600 is the odd one out with a float level of 7mm. Mine were set nearer 10. I don't know enough about this to know what effect that would have?

I've just about finishing putting them all back together but haven't had a chance to run it yet. I'll do that in the morning.

Anything else obvious I've missed?

Last edited by donlamb; 09-16-2014 at 02:24 PM. Reason: Grammar
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post #7 of 61 (permalink) Old 09-17-2014, 02:21 PM Thread Starter
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Still no difference after servicing my carbs, 5-6 turns to maintain idle.
I tried the idle screws that came in the kit as they're quite different to mine but made no difference.
Has anyone seen this type of idle screw before? Are they particular to the 40 DCOE 44&45?

I'm at a bit if a loss now. Maybe air leaking in through mounts or damaged idle screw seats?
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post #8 of 61 (permalink) Old 09-17-2014, 08:39 PM
These are the same as the screws that came out of my 1600. Unfortunately this motor and its carbs won't be in the road anytime soon so I can't offer any suggestions...

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post #9 of 61 (permalink) Old 09-17-2014, 08:50 PM
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Those are the emmision style needle tipped air correction screws. Normally they will adust somewhere areond 6 turns off the seat.


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post #10 of 61 (permalink) Old 09-18-2014, 01:31 AM Thread Starter
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Quote:
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Those are the emmision style needle tipped air correction screws. Normally they will adust somewhere areond 6 turns off the seat.
Thanks, finally I have a clue!
How can I tell if my carbs are emission ones? Were all DCOE 40 type 44 & 45 emission carbs?
I read somewhere about the size of the hole above the rear inlet but it wasn't very clear.
These are mine....
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post #11 of 61 (permalink) Old 09-18-2014, 01:33 AM Thread Starter
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This shows the holes above the inlets...
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post #12 of 61 (permalink) Old 09-18-2014, 08:10 AM
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Were all DCOE 40 type 44 & 45 emission carbs?
My definition of an emissions Weber is one where the idle/progression circuits are fed from the well. The idle/progression circuit of the DCOE 40 type 44 & 45 is fed from the float chamber and it requires the same jetting as classic Webers. 50F15 are type 1 idle jets. they are intended for classic Webers and they were original in these carbs. They are much leaner than the normal 50F8 that seems to work best in Alfa 2L motors. I would try a set of 50F8's.
Some later classic Webers used the same idle screw as the emissions Webers and it appears that the 40DCOE44/45 is in this category.

There has been a lengthy discussion on this in a thread with emissions webers in the title.

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post #13 of 61 (permalink) Old 09-18-2014, 08:42 AM
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Ed may be correct. The 44&45 combination was a earlier DCOE variation. These are fitted with the emission type coarse needles fitted over the throats as pictured below in my first photo. These are a pair of 44/45 restored for Fred Frey. Yours appear the same design. As such the fine needle tipped REAR air correction needles (4) are correct for this variation. The third photo is these Webers fitted with the original cold air box bottom.
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post #14 of 61 (permalink) Old 09-18-2014, 02:28 PM
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The 40DCOE44/45 was original equipment for Giulia 1600 Supers. They had F16 emulsion tubes, 117 main jets and 180 air correctors. If I had read the complete thread before I posted I would have seen that they are being used on a 1600, so the original jetting should be good. But 6 turns out for the idle mixture screw is unusual. 3 to 4 turns is normal for the ones that I have adjusted.
If you want to try a richer idle jet then 50F4 is one step richer followed by 50F2 then 50F13

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post #15 of 61 (permalink) Old 09-18-2014, 02:36 PM
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Ed, if you start with the needles over the barrels closed, all adjustment with the fine rear needles, you can end up with them 6 turns off the seat. Yes, I know that's not the way you are "supposed to do it", but many prefer to forget the perfectly clean idle with different cams or in racing, and begin with the forward needles closed, using the fine rear needles only.


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