CS runs with issues but can't find the problem

Niels Schoon said:
Hi All,

I would like to get some advice.

Situation: car has run perfectly for many km's, but suddenly start to stutter.
Have cleaned the carbs, vacuum is all okay. Have replaced ignition with 123igntion. Also the alternator has been revised.
Car runs for 5 km better (still a bit slow on acceleration) but after a while stuttering is back. Even to the extent I hear sometimes the firing in the exhaust.

Question: as I have done all cleaning and have seen the jets are clean and the acceleration tubes also etc, could it be related to an electric issue ? Mass somewhere playing up or other ? Any help appreciatted.

Thanks, Niels
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Since I am not that familiar with the 123ignition you installed, I resisted commenting on your problem.

Upon first impression, some of your problems seem like textbook fuel starvation issues, possibly due to a weak fuel pump or even clogged fuel lines. Carburetors can be problematic, but from what I have read, your symptoms do not seem to point directly to the carbs. Frankly, if the carbs had issues, including low float levels or floats that stick, or plugged fuel or air passages, I would imagine the problems would reveal themselves under most driving conditions and not after traveling a decent clip.

The fact that the problem evidently occurs after driving a lengthy distance, also suggests something heat related. On that note, a weak ignition coil will often mimic a weak or failing fuel pump. A weak coil will often demonstrate its weakness after it heats up. You did not mention anything about the coil or whether it is fed voltage via a traditional ballast resistor. The latter may be almost indestructible, but ceramic can break and metal can fatigue. I omitted any diagnosis of the 123ignition. It probably does a great job even when matched with a sub par coil. But, to the best of my old school thinking, it still needs a coil to function - properly. Hint, don't overlook either the coil or the ballast resistor that might possibly feed it. Even if the coil does not rely upon an external ballast resistor and looks pretty enough to adorn a wedding cake, it would be simple enough to swap it with another known-to-be-good coil to eliminate it as a possible culprit.
 
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My car has the same stuttering problem in the same RPM range. It has Zeniths and a 123Ignition and a Bosch red coil. There's a FAQ buried in the 123 website that mentions which coils should be used with the ignition. There is also a mention that if the voltage regulator is sending out very short overvoltage spikes, the distributor will go into protection mode and cut out briefly causing the stuttering. The spikes are too short in duration to see with a regular volt meter. My car had a decades old voltage regulator, so I was hopeful that a a new one would solve the problem. A new Beru regulator was installed along with some carb work, and the stuttering went away for a couple of days. Now it's back. Maybe it's an infant mortality problem with the new regulator or the distributor has a fault or the the carbs still aren't right. The new symptoms are spark plugs wet with fuel, but not carbon fouled, and pulling a plug wire off from any of the front three cylinders has no effect on the idle. The stuttering happens whether the ballast resistor is used or not. 123 suggests removing the alternator belt and driving on the battery as a test to see if the regulator is the problem.
 
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Thanks all for the advice. I will replace coil and regulator to eliminate those as possible errors and come back to you all.
Also synchronising of the carbs will be done in the next few days.
 
lsquaredb said:
My car has the same stuttering problem in the same RPM range. It has Zeniths and a 123Ignition and a Bosch red coil. There's a FAQ buried in the 123 website that mentions which coils should be used with the ignition. There is also a mention that if the voltage regulator is sending out very short overvoltage spikes, the distributor will go into protection mode and cut out briefly causing the stuttering. The spikes are too short in duration to see with a regular volt meter. My car had a decades old voltage regulator, so I was hopeful that a a new one would solve the problem. A new Beru regulator was installed along with some carb work, and the stuttering went away for a couple of days. Now it's back. Maybe it's an infant mortality problem with the new regulator or the distributor has a fault or the the carbs still aren't right. The new symptoms are spark plugs wet with fuel, but not carbon fouled, and pulling a plug wire off from any of the front three cylinders has no effect on the idle. The stuttering happens whether the ballast resistor is used or not. 123 suggests removing the alternator belt and driving on the battery as a test to see if the regulator is the problem.
Click to expand...

Your comment on the voltage spikes is interesting. I suspect the tolerances for our voltage regulators do not conform to the modern electronics in the 123. I just replaced my voltage regulator a few months ago, but when it went the alternator was outputting more than 19 volts into my car. If this were to happen again, it would fry the 123.

I'm installing a voltage meter to guard against this, but this makes me wonder if some sort of voltage suppression also might be in order.
 
When all else fails... start at the beginning- no matter how juvenile, gas, spark, air. Since you have the Zeniths I'm thinking the engine was running well with stock parts, regular plugs (nothing "high performance") cam driven fuel pump, points, etc. When I feel completely screwed I start putting everything back stock, check the compression, use the right coil for the base ignition, check all the ground wires around the distributor and coil and see what you come up with. The only black-magic piece that has caused me problems -sometimes- is the cam driven fuel pump so you can buy a 15.00 cheapo electric fuel pump and mount it in the trunk to eliminate that diagnostic hairball.
 
So, I've barely scratched the surface on this stuff, but another suggestion is to hook up your laptop to the 123 and launch 123 tune. I needed a usb extension cord to make this work, but I leave the hood open a crack, run the wiring through the passenger side window and set the laptop on the passenger seat.

I think you can set the rpm stopwatch to begin in an area where the car runs well, and to end in a range above the stumble rpm. Then drive the car. This should log the 123 data which includes both the ignition advance (total) and the ignition coil amperage. Not sure how many logs the software will record, but in theory this should be helpful.
 
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