Does timing shift.

[Gmg31]

Renault 1560 federal engine

When I finished my restoration I had my car professionally tuned and she ran beautifully. But now after 900 miles there are a few frustrating issues.

During acceleration between 2000 & 3000 revs she is pinking really loud and appears to be a little hesitant.  I would say that above 3000 revs  she is stunning and flys.

When I stop and turn the ignition off she runs on for a second.

It seems to me that I need to tweak the timing a little but can it really have shifted?

[jbcollier]

Not usually but it all depends on what type of ignition system you are running and how good it was to start with.  Can you provide some details?

[Gmg31]

I have the Pertronix electronic ignition.  The only change I have recently made was to add an advance retard pipe. But she was already pinking then and I fitted it in an attempt to reduce it. 

[jbcollier]

IIRC, the vacuum unit on the Renault is an advance unit (unlike the TC/S).

Is the pinging only on full throttle?  Or, part throttle as well?

[Gmg31]

Only on hdull throttle.

[jbcollier]

What is your timing setting at idle (vacuum disconnected) and at 2K, 3K and 5K?

[EuropaTC]

I'll start off by saying it's many years since I ran anything with a vac. advance, so if this is a dopey suggestion, please cut me some slack 

Normally timing doesn't move at all once set, so my take would be that something's changed, either you've done it inadvertently or maybe whatever internal advance the Renault distributor has might have decided to stick on full advance.  That's based on the comment that it's pinking at lower revs (over advanced) but going well on high revs where normally you'd expect to get maximum advance.

JB's suggestion to plot a "revs vs advance" chart should tell you if you're effectively getting full (or almost full) advance at lower revs. If that's the case then I'd be looking to see if there's something broken/sticking with the timing advance weights or springs in the distributor (assuming the Renault uses weights that is ?)

I also found this service bulletin in my files which was issued for the S2. I've no idea if the advance data is relevant to your engine but I'll post just in case it is.

[Gmg31]

Thanks for your advice guys.  I will work through this during the week and let you know how it goes.

[BDA]

I wonder if the obvious might be happening. Is the distributor securely locked with the pinch bolt? Just a thought...