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Discussion Starter #1
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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Looks like air leaks past the throttle. Do you have the OVS inlet on your manifold (small nipple on #1)?

 

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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.

Andrew
 

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Discussion Starter #6 (Edited)
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?
 

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Discussion Starter #7
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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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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Discussion Starter #10
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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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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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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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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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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Discussion Starter #16
I found that thread about "emission" webers. It did go off topic for a while but I think I get it. My 44/45s are classic webers with a slight emission twist (the stepped mixture needles and the idle air bypass needles). Correct?
I'm slightly confused as to whether I'm supposed to be just locking the idle air bypass needles closed or not?

So if 5-6 turns is ok then I think everything is good...apart from one of the idle circuits is blocked. That mixture needle has no effect and the cylinder fed by this throat seems to be running roughly, and draws less air when measured with a synchrometer. A good clean will help I hope.

That aside, I am hoping to swap out my 1600 for a 2.0L that I have bought and will be rebuilding soon. It's going to hopefully be a fast road engine, hotter than standard but not a race engine. Are these carbs going to be suitable?

It's hard not to ask too many questions in one hit. Comes from being new to these things.
 

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If your forward needles are seated, then yes, 5-6 turns off the seat is Ok. The CORRECT adjustment with these is to close the rear needles, and get a rough adjustment with those over the barrels first. This is usually much like single adjustment classic (old) Webers, 3/4 turn off the seat. Then locking those down, get a fine adjustment with the rear fine needles, often in the four turn off the seat.
That aside, most users don't bother and leave those coarse needles closed, doing all adjustment with the fine needles.
Now, if you are planning on a performance 2 L, you are right on the edge of needing a set of 45DCOE's. This can be calculated by choke size as compared to displacement.
With 40 DCOE's, the primary choke airfoil gets pretty flat and poorly shaped past 34 mm. This is not so much an issue if the engine is moving a lot of air over this poorly shaped airfoil at high rpm, but midrange where mixture may suffer. I run a set of 40's on a 1600 race engine with hand formed chokes of 35.2 mm, as this same engine with 45DCOE's with 35 mm chokes has less low end torque. For this SPECIFIC application, 40's are better than 45's. With a 2L pulling more air, you may be better off with 45DCOE's. My GTA engine (1600) runs 45DCOE14's with 35.6 hand cut chokes on the street, and 38 mm on the track. I site this as an example of application for ease of use.
I can run the 38 mm chokes on the street but the engine does NOTHING below 4700 rpm. With a 2L this is less critical, and again depends on the design of the particular 2L.
Some of my Weber customers are comfortable with the high rpm performance of 2L's on the street with 40DCOE's while others prefer 45DCOE's.
A simple 2L street build, might try 40's on an unported manifold, and if they feel they need more, go to 45's, opening up the manifold, starting with the SAME size chokes.
You do not need to build the final version of your 2L in one shot.
I hope this helps. Your 40DCOE 44 & 45 are nice Webers. Those I pictured are now on a 2L.
 

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Discussion Starter #18
That's great info Gordon, thanks. Like I said I'm new to this it but I'm like a sponge and love to absorb all this information. I've just bought 2 Speedpro Series books, one on Weber & Delortos by Des Hammill and the other Jim Kartalamakis' on the Alfa DOHC engine. Good starting points I hope.
Having a resource like this forum and good people like yourself is invaluable.

One more question about my particular carbs, why is one a type 44 and the other a 45? What makes them different and do they have to be installed in any order? (I noticed yours are the other way around to mine)
 

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I started a thread on the dyno testing of my Spider and it is easy to find. With 40DCOE's and 34mm venturies it makes peak HP of 169 HP at 6200 rpm and the power is over 160 HP from 5400 to 6800 rpm. The torque is over 140 ft lb from 3800 to 6300 rpm. I give much of the credit to Richard Jemison's cams. Richard and I think that there is some more power to be got by installing a less restrictive exhaust. So I honestly don't see a need to go to 45DCOE's. How many road spiders in the USA with Nord engines are making more power than mine. I only know of one and it has ITB FI.
 

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They were designed as a pairing. Internally exactly the same. 44 is front 45 rear. Weber made other pairs with front rear numbers. Mechanically the same, but designed as a pair.
a Harley Davidson might run either a 44 or 45, but the pairing was intentional.

Note in Ed's post above he confirms that 34 in a 40 DCOE is big enough for a 40 mm Weber. He would not do better with 35 mm chokes. He also confirms that 40DCOE's are plenty for most any application. I use some of 45DCOE's on the "mouse" engines, but you can do about as well with 40's. For pure race 2L, 45's are a better choice. If you want to go to custom manifolds, you can go with 48's but Richard himself went with 50DCOE's. Took him a while to get them right, but useful in PURE RACE applications when you get them to work.
Take Ed's advice, and stay with the 40DCOE untilk you see what you have.
Just my opinion as usual.
 
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