Ignition timing

[mark030358]

2cams, you are correct, my poor memory.

Hence why I said the dizzy was standard and not modified.

Cheers
Mark

[Phil.C60]

Just my two penny's worth....AFAIK the weights are all the same weight. The number, as 2Cams70 suggests denotes the maximum advance but at the distributor, so double it for crank degrees. The springs control how much advance at how many rpm, and can be different from one weight to the other. The standard twin cam distributor with Webers has a max advance of 26* at 2500 rpm all in, from a suggested static/idle figure of 12* so the weight should be (26-12)/2 or 7*. A 10* weight will give you 32* fully advanced which is good for a modified engine. What the curve is and when it reaches 32* is anyone's guess unless you are able to run the engine at 1,000 rpm stages and check it with a digital timing light or send it to someone like Distributor Doctor or Bestek and get them to run it in their test rig and tell you. The other issue is that to increase the advance you take metal off the contact point of the weight at the full advance stop. This often gets done without grinding off the original number or re-stamping. This makes buying and using any second hand distributor a bit of a lottery unless it is tested! When I checked as I was refreshing my twin cam I found that my original points distributor had a 12* weight in it! The engine alsohad oversize inlet valves in it (bigger than Sprint but not as big as full race) and 320* duration cams. It didn't run well for the road at all. It now has a 123 distributor running curve 7 (it's a switchable type, not the programmable one), 12* at idle. 24* at 2000, approx. 26* at 2500 then all in (32*) at 4500 combined with a pair of cams from Ken Newman (PH2?) with 280* duration. It's now much much nicer to drive and runs/performs well enough for me!