Bright Spark Magneto company has a complete analysis of the performance of the ORIGINAL mechanical ATD as fitted at Stevenage. This graph if from their web site. The advance experienced by the motor is DOUBLE that at the ATD.
E: Engine Modern Fuel & Ignition Advance
Hi Vince,
See OVR #42 for a detailed analysis and info on how to set up a mechanical (Lucas) ATD: Here are the conclusions: Full Advance - single plug heads is 34 BTDC and twin plug heads 26 BTDC. Full Retard - kick start motors 4 BTDC and electric start motors 2 ATDC.
Martyn
If you need further advice that's all contained in the data base here. I had a look today after fitting my BTH last week I know its early days and when the rain stops I can get a run in to sort things out but starting is not as easy as I expected and in the data base it said pull the wheel forward after inserting the rod as that will eat up 3 or 4 degrees now I had not seen that before i suppose on a racer I had refined it on a rolling road and started on rollers what it said in the database makes sense I will recheck my settings good old data base.
enclosed the smart fire "special" ignition set up for big bore high compression engines.
Is that for twin spark heads?
yes
Those Lucas atd advance curves look just like what you would get on a manual advance lever system. Just like on a series A when you have push the lever forward when accelerating.
There is something that I do not understand about the 'D' curve shown by Peter Appleton above. Naively the advance and retard mechanism in the distributor is just a couple of bob weights and a pair of springs. Given smooth bearings etc then why would this curve depart from a smooth, more or less linear shape? I could be missing something here but it looks to me as though the shape if the curve from about 250 rpm to about 1750 rpm indicates something sticking and then releasing once there was enough centrifugal force to overcome the stiction. It then jammed again before releasing once more.
Good - so it maps EXACTLY to post 32 above
I would say this was also a very common issue with some front wheel drive cars through the 80's where the distributor mounted to the end of the cylinder head on the east/west engines. It is just pure lack of maintenance where the dizzy is mounted horizontally and is difficult to get any oil/lubrication down the shaft and out to the advance weights. I use to remove some from car engines where the advance had seized up solid, resulting in total lack of power and overheating on the engine. At least the ATD's in the earlier engines have a constant lubrication to keep wear to reasonable limits.