Tuning for vacuum isn't a good idea. Lean idles will give the highest vacuum, but you can get a really lean idle that seems stable once it's settled at idle and you then adjust it. But when idling down or as weather changes it can get unstable, or load from something like an AC; it will be unstable.

Best bet is a "how it responds" approach. The leanest idle that's stable under all circumstances, increased load, idling down after revving etc etc.

Lean idles also cause problems with cruise on carbs, since much of the steady cruise fuel comes from the idle circuit.

 

Interesting!

I had problems, about 3 years ago, with hesitation during cruise speed, but I fixed it by adjusting the float level and the problem disappeard.

But it is an interesting idea, since the only adjusting that I have done this year is adjusting the idle mixture because of high CO-Readings (all four screws were adjusted way out, but the car has been running fine for the last 3 years). I only adjusted them roughly to change the CO-Readings from 8 to 4 and it showed no signs of hesitation when driving home that day.

When I think of it, the problem occured the week after the adjustment!

After the car died/impossible to start I changed the idle mixture at the same time as I changed coil and condenser. I noticed that the vacuum was low, so I set the idle mixture at the highest vacuum and I could really hear the sound/rpm increase when I adjusted the front screws to 1.5 turns and the back one 2 turns. I have not been driving far after that, but I have not had any problems so far when the engine reaching working temperature.

Let´s say this caused the problem. Why did it happen after 10 minutes of driving? Why was the car impossible to start? It does not make any sense so I still have my ideas about volt. Perhaps a combination?

 

Heat in the chambers probably. As weather changes and you drive longer, more heat builds up in the heads. If the engine is a tad on the lean side, after more heat builds up the combustion process can get pissy. Then it stalls, and you're trying to restart with no choke on a heat soaked engine that's too lean.

Domestics need more fuel than you think. On the CPG forums this is one of the things constantly getting beat into people....domestic engines want to run richer than you think they do....everywhere. Especially performance engines.

Is this a smog engine? Or were you just using a multigas to tune? If multigas tuning, set it so you have a slight HC with very slight NOx or back the timing off to where NOx disappears, a bit of CO isn't bad but does indicate minor aberrant combustion.....could be too lean or too rich, too much timing or not enough. You typically want to maximize timing (where most power is made on domestics) and run a tad on the rich side.

If it's a smog engine, then set it where it needs to pass, then set it back to where it runs right.

 

I used a exhaust gas analyzer and changed the Co2-level by adjusting the idle mixture screws clockwise (just focusing on passing the Co2-level).

I used this setting when the engine died the week after, and perhaps it had something to do with it. But it occured when driving home from a car meeting. It showed no sign of problem when going to the car meeting (30 minutes of driving).

Then I changed coil, ballast and condenser and it happened again the day after (the car got worse when I put my foot on the gas pedal and finally died.) It was impossible to drive home again and I could only make it run for some seconds and then it sounded crap (like it would run on 3-4 cylinders).

Later that night, I adjusted the idle mixture by using a vacuum meter, but I could still feel that there were something wrong when driving around the neighborhood. The day after I changed to an old Accel coil with higher resistance that delivered more volt to the coil and I could feel that the car felt better (I tried that coil when the car died without result, so maybe it is a combination of idle mixture and coil).

Maybe I still have to adjust the idle mixture more rich, but it feels wrong to adjust something so the vacuum drops!?

The only thing that does not immeditaley affect the vaccum or engine sound is when I adjust the two idle mixture screws on the back of the holley carburetor. So maybe, I already fixed the problem, but I have to drive more to be certain. Anyway, it feels safer to drive with 8 volt to positive side of coil than 6 volt.

You are saying listen to throttle response, etc instead of vacuum? Ignition timing is high on the car. Last time this problem happened it was a bad condenser, but this time the same thing happened after putting in a new one (perhaps bad out of the box?)

 

I've tried using a gas analyzer to tune my car and pretty much came the conclusion that tuning for ideal emissions produces crap throttle response (on my car, anyway). I managed to get it to run really clean, both at idle and no-load high-rpm conditions, but in real world conditions it suffered from lean-misfires and poor throttle response. I went back to tuning for throttle response and power and fixed the problems I created.

 

The engine will tell you what it wants by how it runs. Tuning for vacuum or low emission readings will get you into trouble most of the time.

 

Thanks guys, I will have a look at it later this week. Here is what I think caused the problem:

1. Wrong idle mixture just to pas Co2-regulations
2. Bad ground
3. Not enough volt to coil
4. Perhaps bad condenser out of the box

It makes you wonder when reading this post: "finally called Mallory and, after much discussion, was then told that they indeed had a probem with their condensor supplier and that they estimated that about 25,000 condensors were delivered defective and that yes, this was the source of our problem. They had no idea where the 25,000 condensors went so they had no way of pulling the faulty parts off the market. We discovered that they were installed on new units as well as the spare/replacement parts you could buy separately from Mallory".

"A few years ago and litterally every car equiped with a Malllory dual point had the same problem sometime during the week. If it wasn't so inconvientent on such an event it would have alomost been comical. Every so many miles another car would be on the side of the road and changing condensors. Frankly we started to be worrried we would run out of spare condensor parts. Unfortunately at the time we did not know the real problem and kept replacing the defective ones with new Mallory parts. Otherwise the Mallory distributor is a great part and very reliable."

 

Hello!

I want to mention that when changing the idle mixture for lower emission something probably went wrong. Since the idle speed was to high (transition slots overexposed) I did not tune it right when I got back to the garage. But yesterday, when changing the rpm I immeditaley noticed the effect when adjusting the idle mixture. I went for highest vacuum and then turned them out 1/5 (all four are 1 1/5)

After setting it right, I adjusted the idle speed back to normal. I now have much better response, idle is super, engine feels much quicker and nothing happened when it got hot. But I also think that I had a bad condenser out of the box.

 

I think that with a resistor wire that should be all you need, 9V is about right.

When I had a points system on my 68 302 all the literature I read said use either a ballast resistor/or resistor wire.

The ballast resistor is better , because when cold cranking t has less resistance allowing for an easier start , as it heats up resistance goes up and gives you lower voltage for prolonged coil and points life. The resistor wire is pretty much a constant resistance. If it starts fine cold then I wouldn't worry about the ballast resistor .

 

Yes, the whole purpose of this thread was to find out the ideal voltage I´m waiting for a analogue multimeter so I can be certain. I believe you get some sort of average value on a digital.

Last time I checked I had 7.8 volt on positive side of the coil during idle. I do believe that 9 volt is a bit to much because of volt peaks higher than 9. The funny thing is that I had less volt on the positive side of the coil with a coil with less internal resistance - I thought it would be the opposite.