when its pinging... its very much usually TOO far advanced (retard the ignition timing by heading closer towards TDC rather than before), or simply BAD fuel.
the more retarded then the more gutless its suppose to be. So if its getting more grubby when being advanced... then far out! I'd be suss its a fuel issue then. Check that hte distriutor clamp is firm on the dissy body itself, as well as on the engine block.
heat can cause pinging as well, so running lean would be a major contributor of such. The hotter the motor gets, the sluggish it runs. They say if you can't touch the dip stick cause its too hot, then you know its overheating. It should be warm enough for you to grasp and pull out without burning yourself.
So!
1) get some PREMIUM petrol from a decent servo... like a Mobile rather than 7 Eleven... (greater octane rating naturally cures pinging half the time.)
2) time the motor for factory specs
3) make sure distributor hold down bolts are crazily firm without killing it
4) Rich it up a bit on the carb [IF THE ABOVE DOESN'T WORK]
5) If its overheating check the fan for rubbish in it like leaves, make sure the tin wear looks alright and seams firmly sealed. make sure the cooling fins on the barrels and heads aren't gunked up with oilly mud or anything. If no luck here then post another thread if shes overheating.
heres some good info:
http://en.wikipedia.org/wiki/Engine_knocking (knocking, detonation, pinging... all the same term for same phenomenon)
QUOTE:
"Detonation can be prevented by any or all of the following techniques: the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate; enriching the fuel/air ratio, which adds extra fuel to the mixture and increases the cooling effect when the fuel vaporizes in the cylinder; reducing peak cylinder pressure by increasing the engine revolutions (e.g., shifting to a lower gear, there is also evidence that knock occurs easier at low rpm than high regardless of other factors); "
