33 engine noise

[Lawrie]

Over the last year or so our 33(99a engine) has had this harmonic type noise creep in, mostly on acceleration or power on,
I looked back through the log book for the 33 and see that it was more than likely traced back to one or two distributors.
I had tried lots and always thought (rightly so) that it was related to timing.I even made up a list with the 68 advance in ,it seemed way better but lost a lot of power I thought, and the ford engineers new more than me, thats why they used the 11a adv.
Yesterday we went for a long drive(150 miles) and before we left, I manually set the static timing on the engine @4 deg,( I usually use a timing light.)
So on the way out of town it pinged up the hill so at the servo I screwed the vac brake half way back in and from then on the noise is just about non existent,and quiet in the cab.
All the times before when I tried to fix this noise I always thought it was too much advance and retarded the timing and vac brake together, it never got rid of it.
So looks like the timing needs the 4 deg and the vac adjusted the curve to suit our 91 oct fuel.
I must be getting stupid ,if I just read my ford books that was what they say to do.
The 33 is back being a pleasure to drive
I have written a detailed note on this and put it in my files so when my boys have the 33 in 20 yrs they will know how to fix stuff.
Lawrie