Duraspark distributor - advance questions

The car is geared tall so when pulling hills it is working hard. It is heavy, not like a 10 ton truck but all the all wheel drive mechanics add weight to things. If you are running over size tires, it makes it work that much harder pulling hills.
The engine does not have a whole lot of power in the first place. All those things add up in the wrong direction.
But
and the operative word is but, exactly how are you setting the timing, what do you set it at.
Basically pinging is a diagnostic that says you are running too much advance and probably a poor grade of gasoline.
When you are climbing a hill, the vacuum should fall off and the timing should also retard because of that so pinging if a tendency should be reduced.
At the moment, there are a whole bunch of unknowns.
What can you add to fill in the gaps?

I understand I should back off the initial, however, it really gets lazy feeling when I do, but the pinging subsides completely. I couldn't imagine a family riding in the car, it would hardly move, lol.

macdude443 wrote: The initial timing is set at 9* @ 1600 RPM with vac advance plugged and fender vac switches unplugged. I have the vac advance set so it doesn't start advancing until it gets 6" of vacuum. It is connected to manifold vac as per the firewall diagram.

My Manual, a 1980 manual which is a configuration more or less like the ones used up until the time AMC went south forever says that the correct setting for the timing is 10 +/- 2 degrees at curb idle speed with the vacuum line disconnected. Curb idle speed being 600 rpm.
This establishes the base line for what ever configuration there is that controls timing advance when hooked up correctly.
The charts indicate that at 1600 rpm, there will be an additional 2 to 7 degrees of advance added to the initial settings which is a function of mechanical advance and a vacuum reading of 18 inches of mercury will add an additional aprox. 20 degrees of advance depending on the part number of the vacuum can.
I do not know of an adjustment that allows one to set the vacuum advance to work at any particular vacuum reading that is part of the original car smog configuration.
But even if there is something added to the thing to make an adjustment, a partial throttle cruse setting such as one would have when driving at legal speed limit in hilly Pennsylvania would give more than 7 inches of vacuum at a manifold vacuum port thus advancing the timing for that particular set of circumstances.
As your adjustment procedure does not seem to be the one recommended for setting the timing and the symptom that you are experiencing is that there pinging which can be a function of too much timing advance, I would have to guess that there is indeed too much initial advance.
Granted, I have a 1980 TSM in front of me and there very well might be a different procedure for 1986 that I am not aware of. But your initial timing advance setting is suspect.
One of the performance enhancement suggestions made for a standard distributor run configuration is to select a vacuum can that will give full vacuum advance added at 1 inch of vacuum less then that measured at a curb idle speed. This assumes a static advance setting obtained normally with the vacuum line disconnected (and plugged) when setting the timing used for particular engine in question. The objective being to allow as much timing advance that the engine can used when driving under a partial throttle set of conditions with out pinging.
The octane of the gasoline used to be compatible with the compression ratio that the engine has



Edited by uncljohn - Apr/28/2015 at 12:33am

Yes you are correct, there is a configuration difference between the 80 and the later AMC engines. So the explanation provided is both detailed and appreciated. Thanks.
I do not have a later than 80 manual simply because I never owned one later than 80 but I do have a Chiltons American Motors 1975-1986 manual that I am looking at and the Tune up Specifications say that timing should be 9 degrees before top dead center at an idle speed of 800 rpm.
As far as actually setting the timing, the instructions of this manual simply says to remove the vacuum advance line from the distributor vacuum advance can or mechanism and plug it at the line and set rpm to the number indicated on the under hood sticker. However the chart in that section indicates that idle rpm is 800 rpm for Automatic transmission. And it cautions that this is done to remove any influence that may come form the mechanical advance of the distributor.
It also caustions that if there is a throttle stop solenoid to disconnect it electronically. As this is a generic oversimplification of this device as there are bolt vacuum, electronic and spring loaded throttle stop devices in use depending on the year and whether it has A/C or not and in some cases it is this device properly disabled in what ever fashion is needed to let it function as an idle adjustment speed device. Rather than using the adjustment screw on the carburetor that is generally used for idle speed on earlier versions that adjusts the idle speed.
Improper adjustment of the idle speed stop device is a lot of the drivability problems this engine has had.
So this manual does point out a procedural problem that may exist.
But using your information, with the vacuum line disconnected and plugged that is equivalent to driving up a hill and having the vacuum fall below 4 inches thus no longer affecting the advance of the timing.
(These years AMC cars 'specially the Eagle with Vacuum controls running the drive train) do not carry much vacuum in their systems when running. My Spirit, and 80 was hard pressed to hold 11 inches at idle.
My memory as faulty as it might be at this point in time seems to remember the "Industry" trying to convince us owners that pinging was good.
Enough said there.
But it implies that pinging was also quite prevalent and I never liked it.
The diagnostic section is as follows
Pinging
Incorrect timing
Distributor centrifugal or vacuum advance malfunction
Excessive combustion deposits
Vacuum leak
Excessive compression
Low octane rating of fuel
Sharp edges in combustion chamber
EGR valve not functioning correctly
The compression ratio of the engine is 8:1.
As to upgraded gasoline, todays octane ratings due to the manner in which they are determined are not directly comparable to yesterdays methods. As such I do not use the bottom grade gasoline for anything other than killing weeds.
In 1958, 8:1 compression was considered high, not that there were not higher, it was still high.
A middle grade as far as I am concerned is appropriate at bare minimum for my car(s)
When I build an engine I build a 9:1 compression engine and use the 91 octane premium gasoline available here where I live.
I have built a few Street Performance AMC I-6 engines and they run well and tune well on 91 octane. To run anything less than 91 octane requires de-tuning. Something a person does. In a new car, the engine detunes itself through the use of the sensors and it's computers.
I really do not nor have I had a pinging problem on an AMC I-6 engine that was not resolved by a careful tune or the use of at least a middle grade fuel.
This is my latest:'



Good Luck
And have fun