The link, if you can open it shows an amazing right that French peeps have that no other country allows!

and this is the wind that blows in our area.


The details of its effects and supposed cures are also interesting!
 
I must admit that if it had been me I would maybe have done both of these but I would have done them one at a time to see which had the effect.
Predetonation I would have imagined coming from the timing being slightly too advanced, yet you have advanced the timing but you have done that and it has gone away.:vb-confused2:
It also used to happen when cars first started using lead-free petrol, to the point that a backfire exploded W's BX's front box!
So I retarded it by much more than was originally thought it ought to be. (Later figures given out showed the earlier ones to have been too conservative.) So what fuel are you using?
Changing the dashpot oil would affect it on acceleration and if that is when it used to happen then you would be momentarily making the mix richer than before which I think would also stop it preigniting, but I am not sure on this.

Have you tried the old skool way of measuring the power of your engine under road conditions?
i.e. getting someone to time with a stop watch how long it takes to accelerate from one speed to another while remaining in top gear??

This used to be in all the old skool Haynes Manuals. And not changing gear makes that not a factor. Say from 30 mph to 60?

Done a few times, either on the flat or up a hill, if you can, starting always from the same point?
I had noticed that the pre-ignition "bang" seemed to always occur when trying to accelerate from a low (15-20) speed. I know generally how the SU carb works and I realised that if the throttle was suddenly opened that the dashpot would rise and that if it rose too fast then the "accelerator pump" effect could be lost. So that was the prompt for the 20w/30w change.
I do not know if the head on this 1275 is leaded/unleaded head but I always fill up with "Super" E5 and add a fuel additive "Castrol Valvemaster".

That tip on looking at your plugs and getting the soot line on the earth strap to begin close to the plug's threaded section was a secondary change. It does not seem to have done any harm. The dizzy was NOT moved by the "tuner" so he didn't mess with it at all, he just wound the jet down and filed the needle. I am feeling pretty comfortable with how the thing is running right now so I may cancel my static tuning session with that bloke you don't think much to. :D
 
Last edited:
Just a thought, the jet in an SU isn't adjustable
All the jets are the same size and fixed in HIF 38 carb for instance, just have different needles for different cars
Yes I know. If you wind the jet DOWN the mixture is enriched across the entire needle profile as the needle moves up and down.
Contouring the needle at the relevant "stations" affects the mixture at the station-specific rev-range.
The needle he "made" for the car was a terrible HACK that would have eventually sawn through the jet and buggered that too.
I took his "custom" needle out and put a BDL back in and re-tuned it myself as per the SU setup manual.
Here's a pic of the hacked about needle he made. Se the big notch in it? there's one on the other side of the needle at the other end too and inbetween it is all rough as a bear's bum file marks. Look at the smooth fine end of the needle that he did not mess with compared to the part that he "customised"! :(

1754668611775.png
 
Ha, Ha!
And the silly feck can't even spell whisky properly!!!!! 🤣 🤣 🤣

Yes I know. If you wind the jet DOWN the mixture is enriched across the entire needle profile as the needle moves up and down.
Contouring the needle at the relevant "stations" affects the mixture at the station-specific rev-range.
The needle he "made" for the car was a terrible HACK that would have eventually sawn through the jet and buggered that too.
I took his "custom" needle out and put a BDL back in and re-tuned it myself as per the SU setup manual.
Here's a pic of the hacked about needle he made. Se the big notch in it? there's one on the other side of the needle at the other end too and inbetween it is all rough as a bear's bum file marks. Look at the smooth fine end of the needle that he did not mess with compared to the part that he "customised"! :(

View attachment 347134
Jet doesn't move
Needle goes up and down as you say
Have you tried no oil in the dashpot just to se if its the same ?
 

Similar threads