123Ignition Revisited - Page 4 - Alfa Romeo Bulletin Board & Forums

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post #46 of 56 (permalink) Old 06-22-2016, 06:46 PM
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I have the 123 vacuum distributor. Its advance curves are the same ones as the non vacuum unit, out of which one is the Giulia TI curve which is from a Bosch vacuum distributor.

My intention was that the vacuum distributor, which only costs a few dollars more, would give me more options to optimize timing for everyday driving. I tried several of the curves before finding out that the vacuum advance is ALWAYS active, no matter what curve you select. With all but the Giulia TI curve, it gives way too much advance.

If you don't want to use the vacuum, do not connect it to a vacuum source. I suggest you cap the connection to prevent dirt from getting in.

If you do use the vacuum advance, adjust static timing BEFORE connecting to a vacuum source, or pinch the hose during adjustment.

Yves Boulanger
1974 2000GTV - 1973 Citroen DSpecial - 1969 Lotus Elan S4
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post #47 of 56 (permalink) Old 01-30-2017, 09:13 AM
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I have a 1974 105 GTV 2000 with stock pistons and stock emission webers, 10.3:1 compression, 10.9 mm billet cams, and Air conditioning.

I have currently have the E Shankle-#4255 curve set, it idles poorly (esp with AC), and I have to drive it a bit tentatively to prevent pinging, although acceleration is very good. I had too much back fire through the Webers with curve A 0.231.178.006, which leaves curve 1 0.231.110.045 and curve D 006-’tuning’.

Can anyone recommend a curve that will give me a stable idle, good fuel economy and good acceleration without pinging for my car given the specifications I've listed? This is new territory for me and indeed I've never even set my own timing before (although I do have a Innova digital timing light with tach).

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post #48 of 56 (permalink) Old 01-30-2017, 09:37 AM
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I run the "D" curve with (true) 10.6 pistons and Webers and I have a stable idle and no pinging on premium pump gas. My max advance is 34 degrees but I have run with 36 with no pinging. I ran the Shankle curve with an earlier engine with (supposedly) 10.0 pistons and I had pinging at WOT around 4000 rpm and unstable idle which always climbed to about 1600 rpm. So I suggest that you try the D curve.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

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 #49 of 56 (permalink) Old 01-30-2017, 09:47 AM
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Thank you very much alfaparticle - I will try D and see how I go
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post #50 of 56 (permalink) Old 02-09-2017, 06:48 PM
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Ok reporting back on D curve! for my 105 GTV 2000 (1974) with 10.3:1 compression engine and 10.9 mm billet cams.

I used D curve with 34 degrees advance (at 4500 RPM) and NKG B7ES Plugs gaped at .33". In order to do a thorough test drive I went for a spin of 4,016 km from Perth to Melbourne. D curve makes for a much better drive, more stable (although not perfect idle) and great fuel economy. It did ping just a little under load so I may retard the timing just a little to perhaps 32 degrees and see how I go.

I mostly drove on 98 octane fuel (although sometimes premium 95 RON) and managed some extraordinary fuel economy. My best 8.51 liters per 100km which is the best fuel economy my car has ever done. The average economy over the whole 4,016 km was 10.52 liters/ 100km and I drove over 1,000 km using my air conditioning.

I'm going to write up my road trip (my 3rd time across Australia) at this thread:

Perth to Sydney Alfa Road trip. Sea-to-Shining Sea


Thank you alfaparticle!!! - know doubt your advice has saved me a lot of money on fuel.

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post #51 of 56 (permalink) Old 02-13-2017, 06:37 PM
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I installed the standard 123 distributor in my 1976 U.S. 49-state 2.0 Alfetta which is running Alfa GRP.1 cams (10.92 lift, 246 duration, 83 overlap, Rank 8L), Euro cast iron headers, Wes Ingram's HP Spica pump, totally desmogged but otherwise a stock engine. The 123 is connected to an MSD STREET FIRE multi-spark box with Blaster coil with no ballast resistor. .035" gap on BP6ES plugs. Yes, 123 says you can't do it, but everything works fine (with one exception, noted later). I had quite a time initially adjusting the distributor. I found TDC using a dial gauge on No.1 and turned the distributor until the green light just came on, but that put me about 20 degrees advance at idle! After messing around with it I now have it set at about 3 to 5 degrees advance. My problem is two-fold. First of all I don't know how many degrees advance the M mark represents on this "emissions" engine pulley. As you may know, in stock the engine's set at 6 degrees ATDC (not BTDC), and the Owners Manual and others don't tell what the M mark is! Does anyone out there actually know?

Dumb me, I had the crank pulley off when I installed air conditioning but I never degreed the pulley. To get the pulley off now involves unbolting the engine mounts and exhaust system and raising the engine as high as possible to clear the crossmember because now there's a 6 groove serpentine pulley welded onto the Alfa pulley for the A/C. It's hard enough peering down below the compressor, past the wide belt, and through all the plumbing to see the crank pulley marks. But I'm going to have to temporarily glue a degree wheel onto the front of the A/C pulley and mark the Alfa pulley correctly. Later.

In the meantime it runs well using the distributor curve #1. It does have better torque pulling away off rest at low RPM which is especially desireable when the A/C compressor is engaged. I have thought about trying the "D" curve but I don't think my engine's been modified enough (no high compression, for example).

My second problem is trying to figure out how to make Alfa's electronic tach work with this new ignition. MSD gives you a "tach wire" that must work in some applications, but not with the Alfa. Another suggested hook-up is to attach the tach wire to the wire coming from the distributor, but that doesn't work either. In trying to figure out which wire is which coming out of the engine bay harness I discovered that Alfa's wiring diagram does not show an electronic tach! Presumably the diagram they give you must have been for early Alfettas with a cable tach... Any ideas out there on how I can get RPMs again?
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post #52 of 56 (permalink) Old 02-13-2017, 07:07 PM
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I suggest that you use a timing light with an advance dial like this Xenon Timing Light with Advance
Use the TDC mark, rev the motor to 5000 rpm and adjust the dial until the pointer is lined up with the mark. 36 to 38 degrees should be good for your motor.

I have my 123 driving an MSD 6AL. I can get a good tach signal from either the tach output of the MSD or the black wire from the 123.

My setup worked well for many years but the 123 died. The power swithing device on the circuit board was fried. The MSD folks reckon that they have seen several others where the 123 has been firing an ignition box. They say that the input resistance is too high. I have considered wiring a 5 ohm resistor in parallel with the MSD input but I have not tried it yet.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

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 #53 of 56 (permalink) Old 02-13-2017, 07:29 PM
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Thanks, alfaparticle. I have read your posts often and knew about your failure before I bought this stuff. That's one reason I went with the MSD Street Fire Multi-Spark, hoping it might be "easier" on the 123 (it does put out a slightly lower plug voltage than the 6AL - and I know that has nothing to do with the input resistance...). We'll see. Although I used a standard Crane system on my Montreal with success, I wanted to try a multi-spark system on this car, and now I have it. I'll figure out that tach one way or another. MSD sells a Tach Adapter for sixty bucks or so but I'd like to see if I can make it work w/o. Perhaps I burnt out the tach, I don't know yet.

Despite what everyone (including Wes Ingram) says, those 246 cams work very well with the Spica.
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post #54 of 56 (permalink) Old 02-14-2017, 05:15 AM
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Don't connect the tach wire to the coil with CD ignition - you probably know that. Can you borrow an oscilloscope to observe the tach output waveform and also the waveform on the black wire from the MSD? They should generate a 12 volt square wave.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

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 #55 of 56 (permalink) Old 02-14-2017, 08:41 AM
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Wish I knew someone who had one. I had a nice two channel osc. but sold it several years ago when I retired, thinking "I'll never need this again". No, I didn't hook the tach wire up to the coil, knowing the coil was receiving something like 400 volts from the MSD.

I suppose I can look for 12v from the tach output with a VOM. However, first I need to remove the tach and trace the wire to be sure I have the correct one since it's not shown on Alfa's wiring diagram.
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post #56 of 56 (permalink) Old 02-14-2017, 09:26 AM
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I believe that it is a white wire that carries the tach signal on your car.
I think that the tach module is a current amplifier. I found that if I drove both my tacho and my Zeitronix from the MSD tach output then the signal would be pulled down at higher rpm. I now run one from the tach output and the other from the black wire of the 123 distributor. A tach module would most likely enable me to connect them both the the MSD.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

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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