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Timing Mark wanders on AQ131D

G

goneposa

New member
I recently tried to set timing on my VP AQ131D after changing cap, rotor, points and ignition wires. The mark wanders about 20 degrees, making it impossible to set. Spec is 6 btdc -- but the best I can do is set the low end at 6 btdc then it wanders to somewhere between 25 and 30, then back to 6, over and over.

I've never replaced timing belt or tensioner but suspect this is where I start..... Is this right??
 
Is there a way to determine whether the problem lies IN the distributor?

The rotor returns to stop point when I twist it -- does this mean the advance mechanism is functional?

I'll clean up the distributor springs/weights and belt tensioner today and check the belt and pulley timing marks.
 
Kim is correct!
If the flyweight springs have been compromised, the progressive advance curve will be very erratic, and it will be nearly impossible to set BASE advance.
If the flyweights have become rusted and are not able to move....., you'll see no progressive advance at all.

I would pull the distributor and take it to a shop who owns an old school Sun or Allen distributor machine.
You'll need to provide the progressive advance curve data for them.
They can then re-bush if need be, and they will re-set the advance curve as per your provided OEM specs.

When all is correct, at idle RPM you should see BASE advance ONLY, and ZERO Progressive until above 1k rpm.
Then the progressive will begin and will stop at X,XXX RPM as per OEM specs.

Now set BASE, and then increase RPM as you strobe the timing marks to verify the curve.

All of this is extremely important for this engine.

goneposa said:
Is there a way to determine whether the problem lies IN the distributor?
Your timing light reading has already shown you that there is a problem within the advancing mechanasm.
This is NOT timing belt related.... even with a tired timing belt.
The belt has either slipped a cog tooth, has broken, or is still working!

The rotor returns to stop point when I twist it -- does this mean the advance mechanism is functional?
Yes and NO........, and to a point only.
At the distributor, we are seeing 1/2 of crankshaft angle. IOW, a 10 degree crankshaft error, will show up as only 5 degrees at the distributor.
Using 5 degrees, you can see that this becomes difficult to determine the actual amount of error........., and is exactly why we strobe timing degree markings.

I'll clean up the distributor springs/weights and belt tensioner today and check the belt and pulley timing marks.
I'd recommend that you do one only at a time by focusing on the distributor first.

Once you get that corrected and the timing set, test it, and see what the progressive advance is doing!

Then change out the timing belt and tensioner.
P of E.... "process of elimination".... one item, and one item ONLY until you isolate the problem.
Click to expand...

NOTE: use caution when cleaning up rusty and compromised flyweight springs. The spring value will change with the degree of rust damage.
A weakened spring set will allow the advance to come on too early.
Spark Advance too early can and will cause Detonation.
.
 
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In addition to Kim's comment, if setting BASE advance does not give you the correct Progressive Advance nor the correcct Total Advance, you must take the ignition distributor back, and have it corrected.

However, if off by only a degree or two, make your focus the Progressive and TA.
IOW, if BASE needs to be lowered by 1 or 2 degrees to get the correct P or TA, make that your focus (within reason).
This is the more important advance!
Whatever change you make to BASE, is an identical change to the P and TA.

BASE is what we fire up on, and idle on, and is not quite as important as the Progressive and TA.

Just say'n! :D

.
 
I'm reasonably sure that if the points are replaced with electronic ignition (Pertronix or HotSpark) the ignition timing wandering at idle will totally or almost completely disappear. Seen that before. ;)
 
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