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Discussion Starter #21
I appreciate all your opinions, suggestions and help with this issue.

Update:

I tired increasing the turns of the the mixture screw and I did see an improved idle and was able to reduce the idle speed screw to around 1.5 turn. having the mixture screw 5 to 6 turns OUT from home where about the best idling. During this time I did not encounter any erratic high idle which was very positive.

I tried these settings both with timing set at 4000rpm on the M mark and 1000rpm on the F mark. Have not seen any major difference. What I have noticed is it is very hard to get it perfect on the F mark when idle rpm is fluctuating. A slightest change in rpm can throw the timing by a few degrees. Just as a side note, I run on 98Octane fuel, as the only other alternative is low in octane.


Whatever I tried, I did not manage to get a smooth idle below 1000rpm. It was raining today and could not drive her in the wet and therefore I still need to try these settings for day to day normal driving.
 

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At 5-6 turns were you getting an acceptable idle (and otherwise good off idle performance)? If so then I think your work is done. That said, 5-6 out does seem excessive even for emission Webers. I would be thinking about a vacuum leak. I would try spraying starter fluid or propane (unlit of course!!) around the mounts and seeing if it changes the idle speed. If so, you likely have a leak.

You might also invest in an AFR meter- very handy tool...

You asked about the advanced weights sticking in the Pertronix dizzy and the answer is yes, since the electronic module only replaces the points and condenser the advance weight mechanism is the same as original dizzy. That is not likely your problem but might be worth checking...
 

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Discussion Starter #23
At 5-6 turns were you getting an acceptable idle (and otherwise good off idle performance)? If so then I think your work is done. That said, 5-6 out does seem excessive even for emission Webers. I would be thinking about a vacuum leak. I would try spraying starter fluid or propane (unlit of course!!) around the mounts and seeing if it changes the idle speed. If so, you likely have a leak.

You might also invest in an AFR meter- very handy tool...

You asked about the advanced weights sticking in the Pertronix dizzy and the answer is yes, since the electronic module only replaces the points and condenser the advance weight mechanism is the same as original dizzy. That is not likely your problem but might be worth checking...

I will check for any leaks as suggested.

I do not have a handy AFR meter handy unfortunately. I do think the car is idling slightly rich but I changed the settings so many times that I have flooded the garage with rich fumes which might have effected my head :laugh2:

Thanks about the explanation on the dizzy.
 

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EAS, glad to hear some progress has been made. There are several differences between "classic" and "emissions" Webers. One of which is the shape of the idle mixture adjustment screws and the thread pitch. On the emissions carbs, the needle has more taper and the thread pitch is finer, at least this is the case on the set of 72/73s I am familiar with. This is what I think Ed was referring to many posts ago. The net affect is they normally need to be opened more turns than "classic" Webers to achieve adequate idle mixture strength.

In your initial post, you mentioned the engine revving to 3000 rpm on its own. IMO, that is a different issue than a delay in returning to a normal idle and is indicative of a vacuum or air leak. Since you had the head off and presumably removed the intake manifold for the head skim cut, it is possible (not probable) that the leak is between the head and manifold. This happened to me many years ago and I don't recall details but replacing the faulty gasket solved the problem. The point is, keep a broad perspective when you check for leaks.
 

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Discussion Starter #26
I have been going through the manual to make sure I didn't leave anything out. Port 1 and 4 of the inlet manifold have vacuum feed. See attached marked in yellow

The one on the left is the brake booster supply but I forgot for what the right one is supplying to. Crankcase cam cover vacuum ?? (My distributor does not operate on vacuum)

I could well have a leak from these. Will check tonight.
 

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The fitting on the right has a hose that connects to the cam cover.
On the right front of the cam cover should be a fitting (two 6mm bolts) that has provisions for a large hose and a small hose. The large fitting has a hose goes to the top center of the air cleaner assembly. The small fitting gets a hose that connects to the front 'yellow' fitting on the cylinder #1 intake runner.
 

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Discussion Starter #28
The fitting on the right has a hose that connects to the cam cover.
On the right front of the cam cover should be a fitting (two 6mm bolts) that has provisions for a large hose and a small hose. The large fitting has a hose goes to the top center of the air cleaner assembly. The small fitting gets a hose that connects to the front 'yellow' fitting on the cylinder #1 intake runner.
Yes that's right. Thanks.

I will plug/shut them both and see if anything changes. I also have a can of carb cleaner I will use to check for vacuum leaks.
 

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I'll confess that the fittings our GTV are plugged. It idles a bit smoother without an 'induced vacuum leak'.
 

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Discussion Starter #30
I'll confess that the fittings our GTV are plugged. It idles a bit smoother without an 'induced vacuum leak'.

Slightly off topic, what is the original colour of the small thin hose ? Mine is brown and I am assuming it got replaced with a transparent one and due to the oil it sucked throughout its life it turned to brown.
 

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Yikes. You got me on that one!
I'll search around to see if I can find anything. Perhaps someone else knows? The cars that I've worked on here in the States, and what I've used, is 'standard' black rubber vacuum hose from an autoparts store. Like the same stuff as the big rubber hose from the cam cover to the air cleaner only it's a bit smaller than the diameter of a sparkplug wire.
 

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As you pointed out you changed the compression ration, so jetting may have to be found through experimentation. Some will argue that you don't touch the extra emission screws, but I found I needed to get my Nuova Super to idle properly. I also use the factory mercury manometer ….. don't see how you can make these things work without it …….. but others will disagree.

But here is a little of my research when I did my first emission control carbs about 2 years ago.

Instruction from “Emission Control Weber Carburetor Tuning Manual” page 54-57:
• Set idle mixture.
o Establish an idle at prescribed value for vehicle (e.g. 900 RPM)
o Working on one “idle mixture adjustment screw” at a time, obtain the highest RPM, most stable running as possible
o After all idle mixture screw adjustments complete reset idle RPM to prescribed value.
• Re-check vacuum balance with vacuum gauge.

The following is provided by others and has not been verified:
• Opinion #1: Emission style needle tipped air correction screws normally will adjust somewhere around 6 turns off the seat.
• Opinion #2: 6 would be unusual, 3-4 is normal.
• Opinion #3: 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.
• Addition comment by #3: 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.
 

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Carl, you are correct, BUT there were at least 4 different types of needles used ion DCOE's. 2 are common, one less so and one very odd. I've pictures of them all, and will try to illustrate here. Oldest (non-emission, Italian) 3/4 turn off the seat. Next a medium taper, used on Italian non-emission and emission Webers, 4 turns off the seat. Finally non-serial numbered emission Webers, with the FINE long taper needle is 6 turns off the seat. These 3/4, 4 and 6 are starting points for adjustment. A 6 turn very fine needle may run correctly as closed as 3.5/4 turns or 7 or 8.
The odd needle is brass, not steel, and was on an odd pre-emission 40DCOE107A and some other Webers.
This needle has an "O" ring seal up top. I set these at 3-4 turns out to start.
I'll try finding pictures...
 

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Couldn't find my old pictures so I took new ones. Note that these needles are NOT interchangeable in the Webers that used different needles. The holes into the body throats are different sizes, and the internal needle seats are in different positions. Further, needles must NOT be over tightened on the seat as it is possible to displace the aluminum that forms the seat, and push the needle itself further through the hole into the body throat, damaging the body.
First is the oldest style blunt needle. I've seen some on very old Webers that have even a less pointed tip. These also start off 3/4 turn off the seat. Second is the longer taper mentioned above. Third is the emission very fine needle, and finally is the brass pre emission 107 style needle with "O" ring.
 

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I've restored a lot of Webers over the years, and seen or worked on most all the DCOE variations.
Some rare ones required re-creation of original parts to replace non-restorable components. Many assume that currently available parts will "fit" all DCOE's. While many components are interchangeable, the DCOE Italian Webers changed over time, and one needs to know how they were set up new at that point in time to be able to have them restored correctly. These variations make this interesting work!
 
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