Mark said your engine was a carburettor unit, so presumably it does not have a catalyst or an ECU, only electronic ignition?
If so, do you have a standard distributor? With a vacuum advance canister on the side?
yes a carb unit. DRLA 40FD. no cat. standard distributor I believe.
the advance curve is determined by the mechanical advance system and the inlet manifold vacuum, and the static advance is set by the distributor position.
Now I saw a small bore pipe leading from the carb, just next to the idle mixture screw, into what I assume is the vacuum advance canister. looks a bit like the fuel pump.
One or both mechanical advance springs may be broken - this could cause the advance to come in too fast, which could cause pre-ignition under certain engine load conditions. Check by trying to rotate the rotor arm in the direction of rotation - there should be strong spring resistance, returing the rotor back to its original position.
Not sure where this rotor arm is. I'll have to have a closer look. Probably on Thursday or friday.
I still think maybe the static timing is too advanced. The timing should be around 8° BTDC at idle, with the vacuum advance disconnected.
How is this timing measured and adjusted?
Only two conditions can result in pinking/pre-ignition or detonation - over-advanced ignition, or too lean fuel mixture. As the latter adjustment is usually covered by tamper-proof plugs, I think its ignition related.
The tamper proof plugs sit in the middle of the carb with a small metal tag on one of the screws? If you draw a triangle between the idle mixture screws, its at the top point?
I have a diagram of the carb but at work.
many thks for your thorough explanations.
Update: just read this which helped a lot.
Now I'm curious about adjusting the iginition timing to see the effects. Advice would be appreciated.