Timing instability question

[fizeus]

How stable has to be the ignition timing at idle ?

Do I have to expect a really stable timing or a little instability is OK??
Mine seems to float between 7 and 3 degrees ATDC at 950 RPM on idle.

I ask this because I'm experiencing hesitations and spitting from carb and exhausts and I'm trying to understand if I have a carburation problems or ignition problem and if I have to rebuild my dizzy before messing with the carbs.


My total advance seems to be beetween 28-30 degrees at 6000 RPM and if I move the distributor to make the total advancing fall into the specified range (32-38 degrees) I end up in making ignition point at 2-3 BTDC with the possibility of engine knocking.
Any way past the 3000 RPMs with vacuum hose disconnected wi ignition point became very unstable

Comments ?
Thanks in advance

[Flat6pac]

On a 73 the vacuum hose is a retard for the distributor.
Your distributor should hold a solid idle when set. This sounds like the first thing to look at.
Bruce

[911pcars]

Check the advance weights and springs below the ignition point mounting plate. This area requires lube to make sure parts work. Otherwise, ignition advance is wonky. in addition, apply a drop or two of oil under the felt disk at the top of the distributor shaft. Remove rotor to access.

Sherwood

PS: Distributors w/o periodic maintenance may have worn distributor shaft bushings which may result in inconsistent/random ignition timing.

[manbridge 74]

Timing should be steady like a rock.

Search around for some good threads on distrib rebuilding.

[T77911S]

shaft play could be the issue.
check the plate the points bolt to

it could also be as simple as grounding.
the points have a wire that connects to ground inside the body of the dist. from that point on the connection is just metal to metal. that metal builds up oxidation or corrosion. clean all those places where the ground signal is trying to make it back to the CD unit and that can help.

I did this on my 77s.
mine use to jump around, especially when setting the timing. even to the point the engine would very quickly shut off and then back on.
the dist body to engine case might be the biggest place to clean. you need a good connection here.

[fizeus]

Originally Posted by T77911S

shaft play could be the issue.
check the plate the points bolt to

it could also be as simple as grounding.
the points have a wire that connects to ground inside the body of the dist. from that point on the connection is just metal to metal. that metal builds up oxidation or corrosion. clean all those places where the ground signal is trying to make it back to the CD unit and that can help.

I did this on my 77s.
mine use to jump around, especially when setting the timing. even to the point the engine would very quickly shut off and then back on.
the dist body to engine case might be the biggest place to clean. you need a good connection here.

Ok... i have to suppose you were next to me while i was trying to set the timing, because you described very well simptoms of my dizzy.

I had also noted that the more i accel the more timing became unstable and this make me think at worn bushings problem.
The shaft anyway seem not having side-to-side play, just some axial and this should a clear symptom of worn washers.

Electical connection should be ok because I had oiled the felt inside the shaft different times and ohm meter do not show high resistance values (this measure was taken with engine off, so when the engine is on and the dist is moving there could be a different scenario).

Anyway the poor acceleration performance and the amount of pops from carbs and exahust make me think that the dizzy has some problems...

I 'm ordering a rebuilding kit from partsclassic, our host seem to not have those kits in catalogue.
I still haven't overhauled the dist because i prefer to have all necessary material before removing the distributor.
I'm still minding if also order a new pinion, just in case....

I'll post my results as soon I had news.
In the meanwhile.... as always thank you all!!

[T77911S]

use a wire brush on a grinder to clean the shaft on the dist.

pops could be mixture.
order a colortune to check mixture.