What does this mean?

[Bakdraft007]

In this Photo of a Fedral stag information plate, its says the timing is 4 degrees After Top Dead Centre? Really? Clearly I am missunderstanding something.. please educate me.

American timing.png

[trunt]

Federal Stag’s have vacuum retard, at idle it retards the timing to keep emissions down, without the retard the timing is probably nearer normal. When driving its gets less and less effective due to where they tap the vacuum and the aggressive centrifugal advance they have is retarded which brings it back.
think of vacuum advance being additive,
And vacuum retard subtractive.

Most dump the retard system!! But you must not use the same vacuum tap on the carb for advance, it’s different.

terry

[Bakdraft007]

Federal Stag’s have vacuum retard, at idle it retards the timing to keep emissions down, without the retard the timing is probably nearer normal. When driving its gets less and less effective due to where they tap the vacuum and the aggressive centrifugal advance they have is retarded which brings it back.
think of vacuum advance being additive,
And vacuum retard subtractive.

Most dump the retard system!! But you must not use the same vacuum tap on the carb for advance, it’s different.

terry

Fascinating, although I am not sure on how it keeps emissions down. Surely firing an engine while its not compressed would lead to incomplete combustion meaning you produce less carbon monoide but more carbon (soot)

[trunt]

It runs hotter, burning more pollutants and the retarded ignition makes it idle slower so you need to open the throttle butterfly’s more to bring the idle speed back up. That brings more air in which flushes out unburnt fuel (hydrocarbons) from the inlet manifold.

I have nursed a car or two through federal emissions!!

Terry

[Bakdraft007]

It runs hotter, burning more pollutants and the retarded ignition makes it idle slower so you need to open the throttle butterfly’s more to bring the idle speed back up. That brings more air in which flushes out unburnt fuel (hydrocarbons) from the inlet manifold.

I have nursed a car or two through federal emissions!!

Terry

It runs hotter No wonder it got retired ealy across the pond

[flying farmer]

I read somewhere that a federal Stag started from cold in 70degree F temperatures would boil if left to idle,the retarded timing was that bad.
I believe the retard was linked to a temperature sensor that removed the retard if the temperature got over a certain limit and that let the idle speed increase to cool down the engine.
More things to go wrong, and they probably did on a regular basis
Neil

[trunt]

Not seen that Neil but some of the fiddles were a joy to behold.. On the 68 TR250 there was retard and advance. The retard was simply a valve that only let vacuum into the retard module when the throttle was at idle, as soon as you started to press the accelerator it closed the valve and immediately took the retard off. Needless to say the valve is impossible to find.. who would want it!

But to get it through emissions I had to manually retard it (I replaced the retard module with a knurled nut adjuster from another car) and bump the idle up quite a bit.. It always passed despite the higher 9.2 compression and TR5 camshaft but I would need to take it on a cold day or the thing would overheat!!

Terry