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Discussion Starter #1
Hi
Just bought the 123 tune distributor. Car is a 1974 spider weber conversion. Based on the information from the bulletin board (grateful as ever) i've made a couple of curves, and just wanted to make sure that these were reasonable starting points as I set up the tuning.
 

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The lower one is more likely to give you a stable idle speed at about 800 rpm. I would have all of the advance in by 4000 rpm.
 

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Discussion Starter #4
Thanks, that's very helpful. Another question, if I was to load two curves, 1 using the parameters that you described with an essentially linear transition, what sort of tweaks would be logical on a second curve to try to optimize ordinary road driving performance using ethanol containing gas as well as ethanol free when I can find it.
Thanks
 

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You could set a higher advance at idle which would give you a bit more advance everywhere until you max out. Within limits, more advance in this range will give you better acceleration and gas mileage. Some dyno work on race engines has indicated that the max advance at say 4000 rpm should be higher than the advance at maximum rpm so you could play around with that.

If you experiment with the maximum advance, you should probably do it with lower octane fuel than you plan to use. Then you will have some safety margin against pinging. I fill up with 93 octane and I did my tests on a 50/50 mixture of 93 and 89.
 

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I would not experiment but adjust this on a dyno. That is the main advantage of a adjustable curve, use it to its full potential imho. Is not very expensive, and allways cheaper than a ruined engine.
 

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I would not experiment but adjust this on a dyno. That is the main advantage of a adjustable curve, use it to its full potential imho. Is not very expensive, and allways cheaper than a ruined engine.
I would agree with this on a high output or racing engine but not on a basically stock engine. These motors will run reliably on a range of max advance settings and it has been discussed in other threads.
 

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But Mad North-Northwest
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Yeah, no need for a dyno for a near stock engine.

Tom Sahines published his recommended curve for the 123Ignition. It's safe and works well as a good starting point. That's what I'm using on my Weber'd 1750.

From Tom's notes:
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RPM LIMIT 6500 (or less if you are concerned about over revving your motor)

point 1 500 rpm 6 degrees

point 2 1000 - 6

point 3 2000 - 20

point 4 4500 - 38

point 5 8000 - 38 (dont worry this can never happen as the rev limiter
will be your actual maximum)
 

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I would agree with this on a high output or racing engine but not on a basically stock engine. These motors will run reliably on a range of max advance settings and it has been discussed in other threads.
I do not agree. In the first place then there is no need to buy one off these in the first place for a stock engine, a normal 123 with one of the stock settings will do just fine. In the second place are the fuels these days having other burning caracteristics then back when the cars were new or not so old, and may need other advance timing. I would say get the most out off the purchase.

a stock engine can also be ruined with bad ingition timing and/or advance...It maybe take longer and have less damage then a race engine going bad at high revs and full load, but still...Why bother if it is ""just"" a stock engine ?


But it is your car/engine, your money, have it your way. Just adding my 2 cents..
 

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Discussion Starter #10
Well, the 123 distributor is in the car, set up per the instruction manual. The car (1974 spider) has not been been started for about two months since I replaced the head gasket. It was running fine before that.

In setting up the new distributor, I rotated the engine to TDC on compression, with the index pointing to the P mark on the crank pulley. Intuitively, I would've expected the distributer cap contact for lead number one to be facing the rotor (this engine has the oil pump drive rotated 180° so the distributor rotor faces rearwards at TDC). However, to get the LED light to come on, I had to rotate the distributor body perhaps 15° Anti CW from this point. When the distributor is positioned either way, the car occasionally fires but it won't start. Fuel pressure is good. I suppose I should probably check for spark and tomorrow I'll try to get one of those gadgets you can put in between the spark plug leads and the spark plug (don't want to bugger up ignition system by running it with plug unscrewed from head). If the fuel is okay, and I see a reasonable spark (and I have no reason to expect that to be a problem) the timing must be the problem. I also might just get a new set of HT leads and spark plugs just in case. These havent been changed for about six years.

I have seen in other threads varying opinions about setting up this distributor. Some have had no problem just following the instructions in the book. Others note that there seems to be no relationship between when the LED lights up and ignition timing. This is rather confusing to me.

Anyhow, if Im making any obvious mistakes I would be very grateful for some input from the experts out there.

The curves I'm using can be seen in earlier postings on this thread.

Mike
 

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I had the same problem with LED set up on my 123 Tune on my mildly warmed '72 GTV 2000 and after playing around, and double checking the drive was seated properly, with no luck I ignored the std set up.

I rotated the dizzy until I got it running then went straight to using a cheap variable timing light to see where it was. A good feature of the tune version is you can set the static timing at TDC (reduces starter load and kick back), lock it down (forever) and mod the cure for high advance at idle which smooths it out, then return to your curve as the revs rise. I'm running what is roughly a Shankle curve with 36deg max and its all in pretty early - about 4000 if I remember correctly
 

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Discussion Starter #12
Thanks for the advice paul. I have a couple of questions. When you say static timg at tdc, do you mean that the engines running at low rpm at idle and the timing light indicates that you are at the P mark on the crankshaft pulley?
Also, when you said you had to rotate the distributor, how much did you have to rotate it? Any guidelines for a starting point and range, I'm guessing it's pretty critical to find the exact position before the car will even start.
Thanks
Mike
 

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Re-reading your thread Mike it looks like you are going through the spark checks so all plugs are firing. Is your old dizzy still working, if so its worth trying that first to check the all systems are ok and warm up.

I see you have already set No 1 roughly at TDC (did you do a quick check that the pointer and pulley are ok?) and tried to advance to get the light on. Maybe try this - put in a 10deg flat line from 500-1500 to start with, fix dizzy with rotor pointing to No 1 lead with No 1 cyl at TDC then rotate in increments, advance first but if its not catching go the other way. If all's well it shouldn't take more than 5-10 degs either way.

I you're bold, liightly tighten the clamp and get a mate to work the starter as you hold the dizzy and rotate it whilst its turning over till it starts then put it to where it keeps it running and lock it. Set carbs etc as best you can then use the variable timing light to check where the timing is at, you will have 10deg in the dizzy so so if it is at TDC then the timing light should show 10 and so on. With laptop connected (don't rely on your alfa's tach) make sure the revs are less than 1500 and the dashboard is showing 10deg, that way you have confirmed you are within the programmed 10deg range, then slacken and rotate dizzy until 10 is showing on the timing light, dizzy will be at TDC, lock it down. If you were a long way away from 10 to get it running I would be surprised but you can adjust the curve to roughly the timing that worked and then do the above to set the dizzy to TDC.

If all's well, modify the curve to 0 @ 500rpm rising to 15 at 1000rpm then rejoin your curve and you should have a reasonable basis to start playing with low rev advance to get best idle and pick up.

Best of luck
Paul
 

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Discussion Starter #14
I got it running, simply fitting new spark plugs seemed to do the trick. I currently have the 123 at 10° at idle speed. I find that I have to wind in the idle speed screw to enable it to idle evenly at about 1100 rpm. Now when driving, sometimes it will continue to build revs after I release the accelerator pedal. don't think that the acccelerator cable is sticking, nor the choke plates. I wonder if I have the idle speed screw put in so far that it is beginning to expose the progression holes for fuel? The engine is also frequently coughing. Spitting back into the air intake.
Any suggestions. I always feel a little bit out of my depth when it comes to changing the carb settings.

Thanks

Mike
 

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More static advance will allow you to back off on the idle speed screw. I have 13 degrees from zero to 1000 rpm (the "006 tuning" curve with 34 degrees max advance) and I can set the idle speed as low as 500 rpm and it idles perfectly but the carbs must be well balanced to get good idle and low rpm performance.
 

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But Mad North-Northwest
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Maybe, but you shouldn't *need* more idle advance. I'm only running 6 degrees (Tom Sahines's curve) and it works great.

What was the story on this car: was it running well before the distributor swap, or did you change anything else at the same time?
 

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Discussion Starter #17
Hi
Thanks for the responses
This is a long story. Spread out in a number of threads. I think it's been running rich for years. I hydro locked (not while running thank heavens) cylinder 3 with head gasket leak couple of months ago and just finished replacing a new gasket. There was a lot of carbon in the combustion chamber, again I think suggesting rich mixture. Head sorted out by progressive auto in Tacoma. Everything de-coked. Was very careful to align cam timing to where it was on disassembly. Compression 180-195 on all four. When reassembling I switched the old fireball ignition with the 123. This is where I am now with surging and coughing back into the air box and idle needing a lot of help with the idle speed screw at 10 deg of advance. Head gasket seems good.

Suggestions greatly appreciated for a logical analysis. Out of my pay grade here. Will try adjusting ignition advance to see if I can back down on idle speed screw. Hoping that less idle screw will put a stop to the surging which makes the car undrivable.

Thanks again everyone

I wouldn't be able to do any of this without your combined wisdom. I really enjoy working on the car.

Mike
 

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But Mad North-Northwest
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Well, it's easy enough to change the idle advance, but like I said mine runs fine at 6 degrees. So I don't think that's your problem.

You didn't change the jetting at all, correct? I'd make super-extra-careful you don't have any air leaks at the carbs. Then I'd suggest you go back and ensure the carbs are properly balanced and tuned again from baseline settings. If you didn't do the tuning steps in the proper order you may have gotten the wrong settings - that's real important.

This procedure is basically what I use: Weber CARBURETOR SET UP AND LEAN BEST IDLE ADJUSTMENT

Note that there are multiple types of mixture screw, so IIRC depending on what Webers you have the ranges listed here may be wrong. But the overall procedure should work.
 

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ensure the carbs are properly balanced
Balance is important. I start by disconnecting the linkage back out the idle screw until it is not touching the throttle arm then back out the synchronization screw. Then carefully screw in the synch screw until it just touches the actuator arm of the front carb. I use a feeler gauge. You may also want to hold the front carb closed while you are making the adjustment. That should get you close enough to run fairly well. Then turn in the idle screw until it touches the actuation arm of the rear carb and give it one more turn. You should not have to turn it in any more than that. Set the idle mixture screws depending upon your carbs. Classic webers start with one turn out from fully closed. Later style carbs 3 turns. Connect the linkage and fire it up. It should idle. If it does, continue with the fine balance adjustment. I short a plug lead on either #1 or #2 cylinder and note the drop in rpm then repeat on #3 or #4. Then adjust the balance screw until you get equal rpm drop. The idle rpm must not be too high while you are doing this - about 1000 rpm. Then fine adjust the idle mixture screws. Turn all 4 in by 1/4 turn at a time until you get a drop in rpm then back them out 1/2 turn and do it again. You want them about 1/4 turn out from the point that makes the rpm drop. Now set the idle speed screw to get 800 rpm. That is it. No stethoscope, no flow meter.

Some motors like more ignition advance than others. I have tried 4 different curves in my 123 distributor and my motor definitely likes more static advance than is found with the old Bosch and Marelli curves. The Jim Kartamalakis curve which was developed for high power engines has a lot of static advance and it works best for me. It is worth a try.
 

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Discussion Starter #20
Great information. Thanks to you both. Could you clarify procedure for shorting plug? I've read somewhere that disconnecting plug wire on running engine can hurt the coil. How do you do this?
Mike
 
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