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post #1 of 12 (permalink) Old 08-17-2019, 04:29 PM Thread Starter
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Weird Condition

We have a rebuilt 1985 2L spider motor with Webers, Centerline distributor, C&B 10.9 intake cam and Alfa cast iron 2 into 1 exhaust. She runs ok, I am not sure if carbs need some tuning, but I am getting there.

Question: when idling I pull plug wire #4, almost stalls, pull plug wire #3, same thing, pull wire #2, no change and pull wire #1, no change.

She idles a bit rough, hunts a little around 800 - 1,000 rpms

Why would pulling plug wires #1 and #2 have no effect on the idle?

thank you,
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post #2 of 12 (permalink) Old 08-17-2019, 05:00 PM
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I assume dual carbs? Are the throttle plates open an equal amount at idle? Keep in mind I know nothing about Weber carbs...

Spark plug wires installed in correct firing order? 1-3-4-2 Clockwise

- - Eric
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~ 1984 Spider Veloce ~
- -~ 1981 GTV-6 ~
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post #3 of 12 (permalink) Old 08-17-2019, 07:04 PM
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Yeah, ghnl is likely on the money...the rear carb throttle plates are probably opening sooner/more than the front, and the rear cylinders are pulling more fuel and ‘carrying’ the front two a little, so there’s less rev-drop.
There are plenty of tips here on the BB about carb balancing by looking down thru the progression hole covers to ensure the edges of the plates are in exactly the same position as the throttle starts to move. You’ll need a torch.
Quick test...Tweak the balance screw between the two carbs a quarter/half turn and see what happens then. You should be able to figure out which way to turn the screw to ‘advance’ the forward butterfly shaft in relation to the rear one...but you won’t damage anything by going the ‘wrong’ way a bit.
Note your starting point so you can put it back if no change.
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post #4 of 12 (permalink) Old 08-17-2019, 07:29 PM
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Yeah, ghnl is likely on the money...
The old 'even a blind squirrel sometimes finds a nut'...

- - Eric
don't read this
~ 1984 Spider Veloce ~
- -~ 1981 GTV-6 ~
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post #5 of 12 (permalink) Old 08-17-2019, 07:48 PM
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Agreed, you probably need to balance the carbs. Some folks do it visually, I use an SK flowmeter tool and DCOE adapter (pics attached) and they've always worked well for me.

Once they're balanced, tuning Webers is pretty stupid easy assuming you've got the right jets in place.

DCOE ADJUSTMENT LAYOUT TYPICAL INSTALL
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Tom

1963 Giulia Spider (1750 engine)
1974 GTV
1991 Spider
Former: 1987 Milano Gold
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post #6 of 12 (permalink) Old 08-18-2019, 05:23 AM Thread Starter
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Yes, dual carbs. I suspected they are not setup correctly, it just makes common sense. Thank you to everybody for the replies. For years I used a Uni-Syn to synchronize the carbs on our 356 Porsche, but will not fit our Alfa.

Gubi, I will probably invest in this setup. It looks like the way to go.

Thanks again to all, the AlfaBB is by far the most helpful car forum out there IMO
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post #7 of 12 (permalink) Old 08-18-2019, 06:44 AM
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I have never used one of those devices. In my case I would have to remove the airbox and plenum to do the tests.

Remove the screw covers over the progression holes and observe the position of the throttle plates with respect to the holes. They should all be the same and preferably covering the first hole so that the first hole is uncovered as soon as you touch the gas pedal.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

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post #8 of 12 (permalink) Old 08-18-2019, 02:37 PM Thread Starter
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Ed,

Do you have x ray eyes when this method is undertaken? I gave it a try and may have gotten close but my eyes are old. The spark plug check works, so we are onto something. All along we have had the engine speed taking about 5 - 7 seconds to return to idle. Now it is worse. Centerline distributor btw
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post #9 of 12 (permalink) Old 08-18-2019, 03:24 PM
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My thoughts, having had this issue with a 1600GTJunior for years

Carbs are out of balance - use/build a manometer or the device pictured above

Throttle plates (or at least one pair) are open too far

Two torches down the throats of each carb doesnít give enough precision to adjust/align the throttle butterflys (I tried this, itís interesting though). I found using a manometer that as little as a 90deg turn of the balance screw (1/4 turn) would put the balance out. You canít see that with your eyes.

I built a manometer using two small bottles, some tubing and water with blue dye in it, keep the combined water level less than the volume of one bottle and it canít enter the vacuum ports (would just clean in anycase)


Check that your dizzy is timed correctly wth a strobe
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post #10 of 12 (permalink) Old 08-18-2019, 05:10 PM
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Ed,

Do you have x ray eyes when this method is undertaken? I gave it a try and may have gotten close but my eyes are old. The spark plug check works, so we are onto something. All along we have had the engine speed taking about 5 - 7 seconds to return to idle. Now it is worse. Centerline distributor btw

Flashlight method will get you close, if not spot on. Takes a bit of farting around to finally see what you're looking for.

You can get close by listening. You understand how the balance screw and the idle speed screw works?

It's Giuseppe's giubos, not Guido's guibos, on my 78 Spider and Sport Sedan
REFRESH CONNECTIONS BEFORE REPLACING COMPONENTS
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post #11 of 12 (permalink) Old 08-18-2019, 05:48 PM Thread Starter
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Flashlight method will get you close, if not spot on. Takes a bit of farting around to finally see what you're looking for.

You can get close by listening. You understand how the balance screw and the idle speed screw works?
My gut is telling me to invest in the STE carb synchrometer, for $45. and another tool made for the job makes sense. I may attempt to fabricate and adapter to hook up an old Uni Syn I have laying around.

Balance screw: adjust the throttle plates between each carb to ensure equal air/fuel flow. The airflow of each carb must match the other carb otherwise the cylinders are not working equally. At full throttle this is of little/no concern

Idle speed screw: Open the throttle plate to allow air/fuel into the intake manifold
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post #12 of 12 (permalink) Old 08-18-2019, 06:16 PM
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Originally Posted by 930cabman View Post
My gut is telling me to invest in the STE carb synchrometer, for $45. and another tool made for the job makes sense. I may attempt to fabricate and adapter to hook up an old Uni Syn I have laying around.

Balance screw: adjust the throttle plates between each carb to ensure equal air/fuel flow. The airflow of each carb must match the other carb otherwise the cylinders are not working equally. At full throttle this is of little/no concern

Idle speed screw: Open the throttle plate to allow air/fuel into the intake manifold
A Uni-Syn works fine if you remove the carb studs or put a velocity stack on each carb.

It's Giuseppe's giubos, not Guido's guibos, on my 78 Spider and Sport Sedan
REFRESH CONNECTIONS BEFORE REPLACING COMPONENTS
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