Who knows about the Ignition timing ?

[sideways60]

Im just trying to get this Clear in my Head ,

1 Does the OEM Etype have a Vacuum RETARD stytem ? , where Inlet vacuum overpowers a Spring ?

2 Does the SNG Upgrade Distributor Keep That Retard System ?

Or does it Become a Vacuum ADVANCE System ? ,

3 Now ive Got SU's , if i connect the SU to the Distributor ive got 2 Opposite Systems Fighting each other ? ,

Pls advise TIA Russ

[MarekH]

Dear Russell,
1/ Yes
2/ Ask SNGB, not us.
3/ That depends where you connect your vacuum hoses to and what they connect to.

The vacuum retard system that Jaguar used had the vacuum capsule connected to a port underneath the left rear carburettor. This only provided a vacuum signal at idle, so once above idle rpm, the retard system provided no retard. Some iterations of this system further only retarded the ignition if other conditions were met. A full list of those is in the tan coloured US Owners booklet.

Vacuum advance systems by contrast take their vacuum source from the manifold, so provide varying degrees of advance depending on throttle opening and engine breathing.

The two systems can only fight each other if both are fitted. Jaguar never used a advance & retard capsule, although Triumphs of the time did. The vacuum capsule superficially looks similar, but there is a tapping on both sides of the vacuum diaphragm whereas normally you'll only see one spigot to take a vacuum hose connection to.

The inlet "does not overpower a spring". The capsule works by pushing/pulling a rod which moves the whole of the distributor rotor assembly a little bit clockwise or anti-clockwise, depending on the strength of the applied vacuum signal. The centrifugal advance is unaffected by vacuum.

kind regards
Marek

[sideways60]

Thanks Marek . Russell

[lowact]

Ignition advance is done to make the engine more efficient (use less petrol). Ignition retard is to make the engine warm up faster, by making the engine temporarily inefficient only when cold and idling (inefficient = less torque, more heat).

The source of the vacuum and the type of distributor must be matched, otherwise they are fighting each other. Ignition advance is by vacuum from above the carb, to a hose connection on the distributor vacuum module that points backwards to the firewall. Ignition retard is by vacuum from below the carb, to a hose connection that points forwards to the radiator.

Ignition retard, the hose from the carb to the distributor is via a thermostatic valve (at the back of the right-side water rail) that shuts off as soon as the engine is warmed up. Otherwise you would be retarded when the engine was warmed up (and idling), creating heat and wasting fuel for no benefit whatsoever.

SNGB offer both vacuum advance and vacuum retard distributors. The vacuum retard distributors are P/N DAB113HE. The vacuum advance distributors are DAB113HEF (“F” on the end). As above, you can tell which one you have by the direction that the vacuum hose connection is pointing.

[sideways60]

Thank you Colin , Think ive Had a Fight going on . Russell