Delay Mechanical Ignition advance

Advance Table, used Bronze Springs and the 20° Limiter.

Hi Jan
Sounds strange that hardest springs would allow all advance to be in by 2000 rpm. Something must be wrong. Are springs perhaps too long? Have they been stretched?
Maybe buy a cheapo MSD spring set and trial and error?

Mikael, its not all in at 2000rpm! It sets in and increases progressively with RPM's from 2000rpm. My objective is to delay the point were the advance sets in another 300-500rpm for a start and see what it says.

I will get some Kits of Springs from Summit whilst I am here in the US anyway.

BTW did anyone ever play with removing material from the Weight to make them lighter and basically get the same result as if increasing the Spring stiffnes?

Jan

Maybe too much initial advance then? Don't know, but sounds strange that most conservative springs give you detonation.

Have you measured advance at 1000, 2000, 3000 and 4000 rpm, so you know if you get what the spring/weight combination promises? Maybe you get something completely different?

Yes it is within a degree or two of the table I posted. But to me it looks like it sets in with 4-5° advance just at 2100-2200rpm like its an on-off function? I checked the weights and they move freely and are not sticking. I cant give a more accurate description/advance schedule currently until I am back home in early September. I was also thinking in direction of lean mixture i.e. a stuck/defective power valve or an other cause for lean mixture during acceleration. But that I will check for once back home. I was in a bit of a rush doing my analyze to be honest. My job came in the way

The pinging I hear is very light and only if the right circumstances are there. Hence my first idea was to work with the advancing Springs, perhaps they were of a cheap Asian origin and had gotten weak during our long trip to France.......

If you want to test if it's advance or fuel leanness related, take the weights off. That will eliminate the advance, if yor still have pinging, it's fuel related.

You're also welcome to drop by, but though Denmark is small, I know we're a few hours apart

thanks Mikael, let me try a few things once I am back home and if I get stuck I might go East. I believe we are planning a trip to see some mutual friends near you anyway soon

no mention of vacuum advance or how it's hooked up if present?

4V & Proud thanks for your question. Vacuum advance is present and actually has no impact on the problem. I tried with and without. The Vacuum advance is only a factor when the throttle Blades are near closed (i.e. cruising with Manifold vacuum deeper than 15 In/hg) and is completely neutral under acceleration were the Vacuum is much less and potentially near zero. Vacuum advance is hooked up to the ported vacuum port on my Holley doublepumper.

Jan

how many tank fulls of fuel has this been going on, can you try a better grade?

you mentioned the car sitting, maybe the fuel went soft?

Something you could try is using manifold vacuum rather than venturi vacuum to operate the vacuum advance.

This is a little outside normal practice and requires a rethink of how your advance works but can sometimes be the way to go.

What it would do is: reduce ignition advance by the vacuum advance amount (say 16 degrees) while cranking, so making starting easier.

Once it fires up it will immediately advance 16 degrees, so you will have initial advance (say 2 degrees) plus 16 = 18 degrees.

When the engine speeds up to what ever your centrifugal settings are the centrifugal advance (say 20 degrees) will be added to the 18 to give 38 degrees total.

Now if you floor the gas pedal regardless of the engine speed and the manifold vacuum drops to 0, as it would under high load, the 16 degrees of vacuum advance instantly gets removed from the total advance, regardless of the initial advance and centrifugal advance settings.

As manifold vacuum increases as the engine overcomes the load the advance increases.

This reduces advance just when the engine is prone to detonating and advances it to the maximum when conditions allow a maximum amount of advance.

All the parameters of advance can be under your control.

You can adjust initial advance by rotating the distributor (remember to add what the vacuum will add when the engine starts).

You can adjust degrees of vacuum advance by modifying the vacuum advance mechanism inside the distributor and you can modify the centrifugal with the springs and weights as you suggested.

Aus Ford, thanks for the suggestion. I am sorry but I rather stick to the standard setup and just get that to work. In other words correting the problem rather than compensating for it. It will work once I sort out the Springs I am pretty sure. I have ordered 2 sets from different manufacturors so guessing there will be a set with just a tiny bit more stiffness and my issue will then be solved. I will line all of them up and make a small test of the Spring Load on each so I am not fighting in the darkness.

Did you actually do what you suggest on your own Pantera? I suppose the benefit of vacuum advanced ignition during cruise is lost then?

Jan

4V & proud, it started on our way home from LMC and I initially addressed the root cause to German low octane Fuel. But it remained after refueling at home with the same Fuel grade as used during Ignition setup initially. So it is not an isolated fuel quality problem. I am more inclined to the fact that perhaps the Pertronix Springs are getting a bit streched due to poor quality and that is were the whole problem lies. As mentioned I am back home early September with 2 kits of Springs in the Luggage (MSD and summit) and will try and sort it out then.

Jan.

It could be a vacuum leek, make sure all your carburetor vacuum ports are plugged and all your intake ports are not leaking. Without knowing your compression ratio,or if you have steel or aluminum heads, pinging at low R.P.M. that goes away as you accelerate (add more fuel and stopping the early cylinder detonation by enriching the mixture )is classic vacuum leek systems failure, leading me to think your air to fuel mixture is the problem. When you set the distributor up, disconnect the vacuum advance.
It is very hard to see some vacuum ports as they are burred under the carburetor or behind the intake, so get the mirror out and make sure you have no leeks. I had a vacuum plug fall off installing a carburetor, it caused a pinging that drove me nuts till I saw the open port under the front of my carburetor through the back window.

Yes this is how I have set the advance to operate on my 351C.

It gives you advance when cruising as manifold vacuum increases during cruise conditions thus operating the vacuum advance mechanism.

The amount of advance produced is in proportion to the level of manifold vacuum, so a small opening of the throttle will only reduce the advance a few degrees, as you open the throttle progressively further (increasing engine load) the advance is progressively reduced.

As load decreases (engine speeds up) advance will progressively increase.

I use low octane unleaded (91 octane)

I doubt it's a due to a vacuum leak since that's the point of driving with the least vacuum. But of course any addition of air leans out the mixture. Worth putting a vacuum gauge on it

I also doubt the ported/non-ported vacuum advance could have an influence. As can be seen on the graph it's only at idle that the two differ. As soon as throttle position is above 10%, the ported port is subjected to full manifold vacuum.

I would still retest the advance at 1000, 2000, 3000 and 4000 rpm (with vacuum disconnected and plugged), be a bit scientific. Your neighbours will love you. Or come by, let my neighbours take the noise, they're used to it :-)

Thanks for all the input. There is not much I can do until I am home again after when I will let you know the result.

Problem solved today. None of the Springs I bought was suitable so I had to retard the initial by 4° to 10° initial and add 4° to the max advance.

10° initial.
24° advance.
34° total all in by 3500rpm.

All it did was just retarding the ignition by 4° during the entire advance schedule to avoid the pinging that occurred at approximately 2000rpm up to 2500rpm. A very annoying thing only happening in that narrow Band of RPM´s. I ran out of time today so could not try the same exercise with 12° initial and 22° advance to check if that would work. After all the more initial I can get the more crisp Idle and Throttle response. I will try one day when I have a few hours and see if it makes sense.

And to answer Mikael´s question wether the Pertronix Spring/weight combination delivers what they promise: Far from! and additionally the max advance limiters is the same story, they cant just be used out of the Box blindly. It all needs to be verified by an Ignition Gun and a RPM measuring device. Some of the items are off by 4°

Hi Jan,
thanks for the info and update on your experiences. I was considering going for a new Pertronix distributor assuming that all would be as one assumes it should be, but now I am getting a Duraspark that has been set up and calibrated in a distributor machine.
Cheers, Tim.

Tim that might be a good idea. I am not familiar with the Duraspark but the Pertronix is in many aspects a good Distributor and you can avoid the Ignition Box as well. If I had to buy another Distributor I would however do a little research and se which alternatives there are and perhaps also choose another one than the Pertronix.

Jan

Maybe I missed it but I didn't see a distributor that would fit. I think the smallest cap was 5" in diameter which would be snug.

I had terrible problem with pinging when I first got my car back on the road. Initial ignition advance was 10deg and I just could work out what was wrong. It knocked awfully around 2000 - 2500 rpm, just as you report.

Oddly the car ran well on choke but this turned out to be a red-herring.

Someone suggested the problem may be that I wasn't getting enough cold air into the carb. So I have temporarily taken out the rear quarter lights. What a difference - clean acceleration, no detonation, even under extreme load. It wasn't that the car ran well on choke - it was that the carb was cold!

I am now having an outfit in the UK make me some blown clear polycabonate vents to fit instead of the quarterlights and am considering fitting one of the Spectre Performance cold air ram style air boxes ducted to these vents.

Murray,
Remember tests have been made that indicate to get any appreciable amount air through the "quarterlights" they need to extend around 4" into the air stream along the car. Hence the so called "elephant ears".

Murray, of course Ambient Air Temperature can affect wether you get a pinging or not. But in my case it came gradually as apparently the Springs in my Distributor had weakened slightly hence the early advancing as opposed to the schedule when I set it up when the Distributor was new. I use a K&N Air Filter which does also sucks Air from the Lid of the Filter. Many factors will affect the potential pinging i.e. Air temperature, Engine temperature, A/F ratio, Spark Plugs and obviously Ignition timing and possibly various other factors. I don´t know your Engine specs but I am surprised if you need to provide colder Air via Elephant Ears to prevent pinging. Is your Engine extreme?

I have made my own Engine Cover with Air openings and Louvrers to escape some of the Heat from the Engine Bay, perhaps that helps. (photo before paintshop ;-) )