detonation advice please- high compression engine 10:1

[twin plugged targa]

Hi all,
Any advice here appreciated.
Car was shipped from USA to UK recently.
Car sounds like it is now detonating at higher revs 4K+ when under load- lead footing!.
This is noticably much more than when in Florida.
Car has not been regularly for 3-4 months but had fuel stabiliser in- perhaps too much?
I have tried some lead addative but no octane booster available in N. France where car is currently.
Air filter is blocked with oil - sucked in when engine running hard- car has a few oil leaks.
tried removing filter, seemed a bit better.
I have a twin plug setup addapted from the 964 setup I believe.
I disconnected both plug leads from top and bottom bank and had a spark/shock from both.
Next step is to remove plugs to examine state of plugs.
Any advice as to air temp/ gas octane etc ( i have put highest available in UK) is appreciated.
Anyone else experienced similar when moving car from different climates?
Thanks Ben

[dean]

Try retarding the timing a hair

[silverc4s]

It sounds as though you may have oil-fouled plugs. Also need to run out all the stabil-ized gas and put in fresh high octane before deciding on further efforts. Advance curve should be examined. Cheers!

[twin plugged targa]

Thanks guys
will fill with high octane gas tomorrow.
I do not have a spark plug socket unless it is 13/16" in which case I need a socket extension!. I forgot what a bugger these plugs were to get to!.
I will also try and get a new filter tomorrow if there is a dealer in the area?- doubtfull!.
I may try and get down top Le Mans and see if there are any specialist garages near there

How would I advance/retard the timing - sorry!
There is a bolt which the distributer pivots on!, should the distributer rotate toi change timing, if so, which way.
The last mechanic marked the rotation position and it is not moved.
The Coils (2)do not have a tight fit on the single HT lead coming out, might this effect it?
- Seems weird the immediate change/increase in detonation!
Thanks again for any advice
rgds`Ben