fiat500 said:

Thanks again John:worship:
I got 3.6 ohms so I hope I'm OK for the moment.

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John jjacob, I have been having an increasingly difficult job starting the beast from cold over several weeks. Hot starts are excellent and no misfiring or other running issues. I know you should not assume anything with an engine, but it isn't plugs, leads, timing or (I hope), the 123 ignition. I thought it was the starting device on the carb but I seem to have eliminated that.
So then I thought back to my overcharging issues of a couple of months ago and wondered if, as suggested by someone here, I had "fried" my lovely Bosch ignition coil. There is a spark at the plugs or it obviously wouldn't drive as well as it does when hot, but the spark is weak and yellow. I have a spare original coil so I may as well try that tomorrow as it's so simple to fit, but I took resistance readings off the Bosch and find the primary is 2.8 ohms compared to 3.2 on the original.
Noting that I did a reading back in December which was 3.6 ohms, do you think I'm on the right track to solving this problem?

Hi Peter,
I would attack this on three fronts.

1. Battery voltage available on cold start.
2. Possible rich mixture on cold start.
3. Failing coil.

1. With a volt meter measure the battery voltage at the battery before starting cold. Make sure connection is clean and tight. You should see 12.5 volts. If you see something less, your battery may not have enough voltage and subsequently you will have less voltage available at the coil.

2. A carburetor that is set too rich on a cold start will be difficult to start. This effect will disappear on a hot start as the fuel is easier to ignite as it gets atomized more easily.

3. You need to check the secondary resistance also. This is measured from the center plug cable tower to one of the side terminals. On a Bosch Blue coil this should be around 7800 ohms I believe. Primary resistance between the two outer terminals should be 3.4 ohms.
The 123 Ignition people state that their ignition system will work with any coil with a resistance of 1.0 ohms or higher. They recommend the Bosch "Blue" coil with a resistance rating of 3.4 ohms. I don't think I would use a coil with a rating less than 2.5 ohms. I also don't think you have to use a Bosch coil. I would target a coil with 2.5 - 3.5 ohms, and make sure the coil is rated as 12v, not 6v or 9v. Do not use a ballast resistor.

Interestingly enough, on the USA 123 Ignition site and the Dutch site they recommend the 126 style double wasted spark coil for use with the version of the 123 Ignition that eliminates the distributor cap and rotor on a 500 or 126 engine. I don't see them recommending a ballast resistor. This would be a resistance of around 1.5 ohms, which is within the spec that 123 recommend. Interesting. If your 123 is the type with the distributor cap, then I think you're supposed to use the recommended Bosch Blue coil or something with around 3.0 ohms.
http://123ignitionusa.com/123-fiat-for-fiat-500-and-fiat-126-special-order-non-stock-item/
http://123ignitionusa.com/123-4240-to-combine-with-123-fiat-double-coil/
http://www.123ignition.nl/products.phtml?brand=fiat 500

As you have pointed out before, there is surprisingly little information provided by the 123 Ignition people. I have the Pertronix system in my current 500 (works great) and the Pertronix folks offer more information which I think is valuable and applicable to any electronic ignition system as far as proper coil testing and use. I copied their information below. They recommend a 3.0 ohm coil.

What type of coil can I use with the Ignitor™? How do I check my coils resistance? (12V negative ground only)
To determine if your systems coil is compatible with the Ignitor, some measurements should be taken prior to installation of the Ignitor. Caution… While performing this test, never leave the ignition switch on for more than 30 seconds at a time.
Set your voltmeter to a 15 or 20-volt scale. Attach an 18 or 20 AWG jumper wire from the negative coil terminal to an engine ground. Attach positive (red) lead of your voltmeter to the positive side of the coil, and the negative (black) lead to an engine ground. Turn the ignition switch to the run position. Now read the voltage at the positive coil terminal. Turn the ignition switch off. If the voltage measured is approximately 12 volts, no resistance wire is present. A typical resistance wire will provide 9 - 6 volts.
The next step is to determine the resistance in the primary ignition. Label the wires attached to the coil terminals and note their appropriate location. Make sure that the ignition switch is off and disconnect all wires from the coil. Adjust your meter to the lowest ohm scale. If you are using an analog style meter make sure to zero the needle.
Measure from the negative terminal to the positive terminal. Write your measurement down.
Now the maximum system amperage can be determined, divide your voltage measurement by your coil resistance measurement. This will give you the system current or amperage.
Four and six cylinder engines should not exceed 4 amps. Eight cylinder engines should not exceed 8 amps. If the total amperage in your system is higher than the amount recommended for your application, you should install a ballast resistor.
Example
Voltage 12
Resistance 1.5
12 / 1.5 = 8
Total amperage 8

What will happen if I leave the ignition switch on when the engine is not running?
Leaving the ignition switch on when the engine is not running, can cause permanent damage to the ignition system, and related components. This does not apply to the accessory position of the ignition switch.

Can I change the length of the Ignitor™ wires?
Yes, the Ignitor wire length may be tailored to your specific needs. Occasionally the wires may need to be extended. We recommend that a 20-gauge copper strand wire be used. Make sure that all splices are cleaned, secure and insulated.

What should I gap the spark plugs to?
The Ignitor has no set specification in which the spark plugs should be gapped at. Every engine responds differently to spark plug setting. In most cases increasing the factory recommended gap by .005 improves the engine performance.

John

Thanks John.
I have now tested the engine with the original Fiat coil which gives slightly better readings for LT resistance and slightly poorer readings on the HT; there is no significant difference in starting ability.
I have the full 12.6 volts at the + terminal of the coil, which drops by about 1 to 1.5 volt when the starter is activated.
I doubt if the mixture could have been significantly wrong but I will experiment with that one.
I am beginning to think that maybe my problem is that I insist on using the car in all seasonal conditions, because when the weather is warmer (I mean 10C rather than -2C). starting is much more decisive.

Timing can also effect cold starting. As an experiment you might try retarding the timing and see if the car is easier to start.

John

jjacob said:

Timing can also effect cold starting. As an experiment you might try retarding the timing and see if the car is easier to start.

John

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Aargh!!!!!
I had thought about that and despaired that it might be a cause of the issue, especially since the 123 instructions had sent me down the path towards achieving the correct maximum advance. It just seems counterintuitive to now rotate things back a fraction as it moves the whole advance curve backwards even though that may help.
Refitting my poor little points distributor seems very tempting just now. But luckily I have the diversionary tactic of removing the cowlings and fitting an alternator at the moment.

fiat500 said:

Aargh!!!!!
I had thought about that and despaired that it might be a cause of the issue, especially since the 123 instructions had sent me down the path towards achieving the correct maximum advance. It just seems counterintuitive to now rotate things back a fraction as it moves the whole advance curve backwards even though that may help.
Refitting my poor little points distributor seems very tempting just now. But luckily I have the diversionary tactic of removing the cowlings and fitting an alternator at the moment.

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I would refit the points distributor just for peace of mind, at least it will be able to eliminate whether the 123 is causing your cold starting issues. It's only a 10 minute job and if you mark up the 123 before removing you will know exactly where to put it back if no joy.

The only problem I can see is that it may not eliminate whether you have a slightly off par Bosch coil because it will probably work better with the points if it was beginning to breakdown. Thinking about further after typing that last sentence, if the problem was the Bosch coil, you wouldn't expect it to be a problem when starting from cold, you would expect it to be worse once the engine has warmed up and the coil has got hot? Wouldn't you?

Vitesse said:

Thinking about further after typing that last sentence, if the problem was the Bosch coil, you wouldn't expect it to be a problem when starting from cold, you would expect it to be worse once the engine has warmed up and the coil has got hot? Wouldn't you?

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True. What I'll do is to retard the 123 a bit tomorrow morning and see how it goes. If no luck then I will stick the old distributor back in and give that a try. The drawback is that it's not all that cold just now.
At the moment this is teh least of my toils as I have an engine with all three of the left hand pieces of cowling removed ready for the alternator modification upgrade. You would be impressed as I got hold of a can of Plastikote for the alternator mounting cowling borrowed off the 650 engine.

Can't go wrong with Plastikote superb stuff. It dries so quickly you can paint the whole of an engine cowling in less than an hour. Did you buy the one that is high temp? It's not VHT but can withstand any heat of the engine without any problem.

You can stick it in the oven to cure it as well, doesn't go to down well when the other half is trying to squeeze a roast in as well though. But I quite like a full roast with engine cowling on the side!

fiat500 said:

True. What I'll do is to retard the 123 a bit tomorrow morning and see how it goes.

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Today I got the chance for a proper cold start with slightly retarded ignition and it fired on first pull.
But ten miles into the journey it was pretty obvious that this was too little advance as I couldn't get past 40mph. So a tiny tweak of advance and the engine was back to its old self.
On my engine there is a very wide range of spark timing over which the car will run well, but clearly, the balance point between optimal starting and running is focussed very narrowly.
So we're running as perfectly as the car has ever gone at the moment.

Back in the late '70's and '80's some American cars had a double diaphragm vacuum advance, timing that would be retarded on starting (ATDC - After Top Dead Center!) and then advance after starting. This was done because of the difficulty in starting in cold weather with an ignition that was advanced for power. I believe Fiat also used this on the 124 series sold in the USA.
Sounds like you have found the sweet spot finally for your 500 timing.
John