Rick Lindsay sez:
:: As for the mechanical advance, a set of springs of varying strengths
:: are available from Moss-TriumphTune in England. A word of advice, order
:: TWO kits! Each 'kit' will do exactly 1/2 of a distributor!
If you have to use two identical springs to get the advance you want, then
yes, you will need two kits. It is more likely that installing two different
springs will give you what you need. Two N lb. springs will give you the
same advance as 1 N+2 and 1 N-2 setup.
In general, though, just make sure that the advance bits in the distributor
are clean and well lubed so that it works like it should. For most Triumph
motors, all the advance is in by 2500 or 3000 rpm [check the chart for the
distrib in your Bentley's], so recurving isn't really a neccessity. One
thing that IS a neccessity is knowing whether you have a vacuum advance or
a vacuum retard or both on your distributor, and whether or not they are
working.
If you change carbs and manifolds, and have no vacuum port you can try to get
by without one if there is sufficient mechanical advance available in the
distributor. Figure out how much total advance you need and by when. Set
the timing to that amount at that rpm, then see where you end up at idle.
You'll probably want somewhere between 8 and 12 degrees for most engines,
though the Mark 2 Spit motor in my Spitfire 1150 is set at 17 BTDC. When
no longer using vacuum advance/retard, one should pin the top plate of the
distributor to the bottom advance plate so that it doesn't wobble about and
throw things off. But that isn't neccesary for general about town use.
Personally, I want an electronic crank fired igniton unit for my autocrosser!
mjb.
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